CAM 20414

Biochemical Markers of Alzheimer’s Disease

Category:Laboratory   Last Reviewed:October 2018
Department(s):Medical Affairs   Next Review:October 2019
Original Date:July 1999    

Description:
Biochemical changes associated with the pathophysiology of Alzheimer's disease (AD) are being evaluated to aid in the diagnosis of AD. Some of the most commonly studied biomarkers are amyloid-β peptide-1-42 (AB-42) and total or phosphorylated tau protein (T-tau or P-tau) in cerebrospinal fluid (CSF). 

The evidence for testing for AD-related biomarkers in patients who have dementia or mild cognitive impairment includes systematic reviews, meta-analyses and case series. Relevant outcomes are test accuracy, test validity, symptoms, change in disease status, morbid events, quality of life, medication use and resource utilization. Most studies derive from select patient samples and define optimal test cutoffs without validation; thus, generalizability of results is uncertain. For the diagnosis of AD, evidence does not demonstrate incremental improvement in diagnostic accuracy over clinical testing. For predicting conversion from mild cognitive impairment (MCI) to AD, limited evidence, including that from the Alzheimer's Disease Neuroimaging Initiative, suggests that testing may define increased risk. Whether earlier diagnosis leads to improved health outcomes through delay of AD onset or improved quality of life is unknown. Therefore, the evidence is insufficient to determine the effects of the technology on health outcomes.

Background
The diagnosis of Alzheimer's disease (AD) is divided into 3 categories: possible, probable and definite AD. A diagnosis of definite AD requires postmortem confirmation of AD pathology, including the presence of extracellular beta amyloid plaques and intraneuronal neurofibrillary tangles in the cerebral cortex.Probable AD dementia is diagnosed clinically when the patient meets core clinical criteria for dementia and has a typical clinical course for AD. A typical clinical course is defined as an insidious onset, with the initial and most prominent cognitive deficits being either amnestic or nonamnestic (e.g., language, visuospatial or executive function deficits) and a progressively worsening cognition over time. A diagnosis of possible AD dementia is made when the patient meets core clinical criteria for AD dementia but has an atypical course or an etiologically mixed presentation.

Mild cognitive impairment (MCI) may be diagnosed when there is a change in cognition but insufficient impairment for the diagnosis of dementia.2 MCI is characterized by impairment in 1 or more cognitive domains but preserved functional independence. In some patients, MCI may be a predementia phase of AD. Patients with MCI or suspected AD may undergo ancillary testing (e.g., neuroimaging, laboratory tests, neuropsychological assessment) to rule out vascular, traumatic and medical causes of cognitive decline and to evaluate genetic factors. Because clinical diagnosis can be difficult, particularly early in the course of disease, there has been considerable interest in developing an accurate laboratory test for AD. Several potential biomarkers of AD are associated with AD pathophysiology (i.e., β-amyloid plaques and neurofibrillary tangles). 

Elevated cerebrospinal fluid (CSF) levels of specific proteins have been found in patients with AD. These include tau protein, phosphorylated at AD-specific epitopes such as threonine 181 (P-tau) or total tau protein (T-tau) or an amyloid-β peptide such as AB-42. Other potential CSF3,4 and serum5 peptide markers also have been explored. Tau protein is a microtubule-associated molecule found in neurofibrillary tangles that are typical of AD. Tau protein is thought to be related to degenerating and dying neurons and high levels of tau protein in the CSF have been associated with AD. AB-42 is a subtype of amyloid-β peptide that is produced from metabolism of amyloid precursor protein. AB-42 is the key peptide deposited in amyloid plaques characteristic of AD. Low levels of AB-42 in the CSF have been associated with AD, perhaps because AB-42 is deposited in amyloid plaques instead of remaining in fluid. Investigators have suggested that the tau/AB-42 ratio may be a more accurate diagnostic marker than either alone.6 A variety of kits are commercially available to measure AB-42 and tau proteins. Between-laboratory variability in CSF biomarker measurement is large.7,8 

Neural thread protein is associated with neurofibrillary tangles of AD. Both CSF and urine levels of this protein have been investigated as a potential marker of AD. Urine and CSF tests for neural thread protein may be referred to as the AD7C test.

Regulatory Status
Clinical laboratories may develop and validate tests in-house and market them as a laboratory service; laboratory-developed tests (LDTs) must meet the general regulatory standards of the Clinical Laboratory Improvement Act (CLIA). AlzheimAlert and AdMark® CSF analysis are available under the auspices of CLIA. Laboratories that offer LDTs must be licensed by CLIA for high-complexity testing. To date, the U.S. Food and Drug Administration has chosen not to require any regulatory review of these tests.

Related Policies
20413 Genetic Testing for Familial Alzheimer’s Disease
60155 Beta Amyloid Imaging With Positron Emission Tomography (PET) for Alzheimer’s Disease

Policy:
Measurement of cerebrospinal fluid biomarkers of Alzheimer’s disease, including, but not limited to, tau protein, amyloid beta peptides or neural thread proteins, is considered INVESTIGATIONAL.

Measurement of urinary biomarkers of Alzheimer’s disease is considered INVESTIGATIONAL, including, but not limited to, neural thread proteins.

Policy Guidelines
There are no specific CPT codes for this testing.

CPT code 83520 (Immunoassay for analyte other than infectious agent antibody or infectious agent antigen; quantitative; not otherwise specified) may be used to report testing for tau protein and amyloid-β peptides.

An example of this testing is the ADmark® CSF Analysis, which tests for phosphorylated-tau protein, total-tau protein and AB42 peptide in CSF. A laboratory website lists this test as being reported with 3 units of code 83520.

There are no specific codes used for testing for neural thread protein.

An example of this testing is the AlzheimAlerttest by Nymox Pharmaceutical Corp. It lists on its website that the test is reported with the unlisted urinalysis code 81099 when performed in urine and the unlisted immunology code 86849 when performed in CSF. 

Rationale
This evidence review was originally created in July 1999 and updated periodically with reviews of the literature by searches of the MEDLINE database. The most recent search covered the period through October 10, 2016.

The clinical purposes of testing for Alzheimer's disease (AD)‒related biomarkers are to improve diagnostic accuracy or to predict conversion from mild cognitive impairment (MCI) to AD.

The evaluation of a biomarker test for diagnosis or prognosis focuses on 3 main principles: (1) analytic validity (technical accuracy of the test in detecting the marker that is present or in excluding a marker that is absent); (2) clinical validity (diagnostic performance of the test [sensitivity, specificity, positive and negative predictive values] in detecting clinical disease or defining prognosis); and (3) clinical utility (i.e., a demonstration that the diagnostic or prognostic information can be used to improve patient health outcomes).

CEREBROSPINAL FLUID MARKER TESTING
Analytic Validity
Analytic validity is the ability of a test to accurately and reliably measure the marker of interest. Measures of analytic validity include sensitivity (detection rate), specificity (1— false-positive rate), reliability (repeatability of test results), and assay robustness (resistance to small changes in preanalytic or analytic variables). Measurements of the cerebrospinal fluid (CSF) concentrations of the amyloid-βpeptide 1-42 (Aβ2), total tau protein (tTau), and phosphorylated (pTau) have high variability within and across different laboratories and across different analytic platforms. Shaw et al reported a 7-center interlaboratory standardization study using Alzheimer's Disease Neuroimaging Initiative (ADNI) participants for CSF Aβ2, tTau, and pTau measures with a within-laboratory percent coefficient of variation (CV) ranging from 5.3% to 10.8% and interlaboratory percent CV ranging from 13.1% to 17.9%.9 Lewczuk et al compared CSF Aβ-42, tTau, and pTau measurements across 14 laboratories in Germany, Austria, and Switzerland. with interlaboratory percent CV of 20% to 30%.10 Verwey et al reported interlaboratory percent CV of 37%, 16%, and 15% for CSF Aβ2, tTau, and pTau, respectively, and within-laborator percent CV of 25%, 18%, and 7%.11 Monge-Argilés et al found that enzyme-linked immunosorbent assay (ELISA) and a multiplex (xMAP) technology for measurement of CSF Aβ42, tTau, and pTau yielded different absolute values for the various analytes, always higher in ELISA, although the values were highly correlated.12 Mattsson et al reported results of an external quality control program for CSF biomarkers.8 Forty laboratories using commercially available kits for Aβ, tTau, or pTau were sent CSF samples for analysis several times a year from a central source. Total CVs between the laboratories were ranged from 13% to 36%.

Clinical Validity
Diagnosis of AD
Most studies have relied on clinically diagnosed AD as the criterion standard. Systematic reviews of these studies are described next; the results are summarized in Table 1. Studies included in systematic reviews are not individually reviewed.

Rosa et al. (2014) conducted a systematic review with meta-analysis of studies of CSF Aβ42 in patients with clinically diagnosed AD.13 Literature was searched to May 2013, and 41 prospective or retrospective, cohort, case-control, and cross-sectional studies were included (total N=5086 patients; 2932 AD, 2154 nondemented controls). Patients with MCI were excluded. Seventy-six percent of studies satisfied all quality domains of the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool. Publication bias was detected. A summary receiver operating characteristic (ROC) curve was generated from all reported thresholds. Pooled sensitivity and specificity were 84% (95% confidence interval (CI), 81% to 85%) and 79% (95% CI, 77% to 81%), respectively. Positive and negative likelihood ratios were 4.5 (95% CI, 3.7 to 5.4) and 0.18 (95% CI, 0.14 to 0.22), respectively; and their ratio, the diagnostic odds ratio, was 29 (95% CI, 21 to 40). Statistical heterogeneity was substantial (I2=68%); studies varied in test cutoffs used and severity of AD across patient samples. Eleven studies (n=1459 patients; 830 AD, 629 controls) reported Aβ42 CSF levels. Mean (SD) CSF Aβ42 levels were 467 (189) pg/mL in patients with AD and 925 (414) pg/mL in controls (weighted mean difference, 450 pg/mL; 95% CI, -600 to -289 pg/mL; p<0.001). However, statistical heterogeneity was considerable (I2=99%).

Ferreira et al. (2014)14 published a meta-review of systematic reviews with meta-analyses to assess the use of CSF biomarker tests for AD after publication of revised AD diagnostic criteria15 in 2011. Literature was searched in September 2013, and 7 systematic reviews were included. None was published after introduction of the revised AD diagnostic criteria, so primary studies were searched. Twenty-six prospective or retrospective case-control, cross-sectional, or longitudinal studies were included. Most selected studies used clinical criteria for AD diagnosis or did not specify. Results for both the systematic reviews and the individual studies are summarized in Table 1. For differentiating AD from nondemented controls, positive and negative likelihood ratios for all 3 biomarkers ranged from 4 to 8 and from 0.1 to 0.3, respectively. For differentiating AD from other dementias, 1 systematic review of 7 studies reported positive and negative likelihood ratios of 46 and 0.09, respectively, for differentiating AD (n=175) from Creutzfeldt-Jakob disease (n=110).16 With this systematic review excluded, positive and negative likelihood ratios ranged from 2 to 7 and from 0.15 to 0.4, respectively.

Cure et al. (2014) conducted a systematic review with meta-analysis of CSF and imaging studies for the diagnosis of definite AD (autopsy-confirmed).17 Literature was searched in January 2012, and 3 studies of CSF markers (pTau, tTau, Aβ42, Aβ40) were identified (total N=337 patients). Pooled sensitivity of all CSF tests was 82% (95% CI, 72% to 92%), and pooled specificity was 75% (95% CI, 60% to 90%). Statistical heterogeneity was not reported, but studies varied by AD definitions, controls (nondemented patients or patients with dementia due to other causes), and test thresholds. Area under the summary ROC curve, constructed using multiple test thresholds, was 0.84.

A 2011 meta-analysis included 119 studies on biomarkers and diagnostic imaging in AD.18 Sensitivity and specificity were calculated for distinguishing AD from nondemented controls, and for distinguishing AD from non-AD dementias with and without MCI, if available. Selected studies of CSF biomarkers used a variety of thresholds, with clinical diagnosis or autopsy as the reference standard. Twenty studies of the Aβ42 CSF marker were included with nondemented and demented controls; pooled analysis resulted in sensitivity of 76% (95% CI, 72% to 80%) and specificity of 77% (95% CI, 72% to 82%). CSF total tau was evaluated in 30 studies with a resulting sensitivity of 79% (95% CI, 75% to 83%) and specificity of 85% (95% CI, 81% to 89%). CSF pTau was evaluated in 24 studies, resulting in a pooled sensitivity of 78% (95% CI, 73% to 83%) and specificity of 81% (95% CI, 76% to 85%). Six studies evaluated CSF pTau as a biomarker to distinguish patients with AD from patients with MCI, with a pooled sensitivity of 73% (95% CI, 54% to 86%) and specificity of 69% (95% CI, 53% to 82%). The combination of total tau and Aβ42 was evaluated in 12 studies, with a pooled sensitivity of 80% (95% CI, 72% to 85%) and specificity of 76% (95% CI, 5%7 to 88%). Comparison of CSF biomarkers, area under the ROC curve was highest for pTau alone (0.85; 95% CI, 82 to 88). Study heterogeneity was due to use of different test thresholds and different assay kits. Sensitivity analysis including studies that used autopsy as the reference standard for pTau resulted in slightly higher sensitivity (82%; 95% CI, 75% to 87%) and lower specificity (57%; 95% CI, 37% to 75%).

Table 1. CSF Biomarkers Performance for Distinguishing Alzheimer Disease From Controls With Clinical Diagnosis Reference Standard 

Biomarkers Studies  Nondemented Controls Controls With Dementiaa
  Sensitivity Specificity Sensitivity Specificity
Aβ42    
 Ferreira et al. (2014)14 SR 80% (73 to 85) 82% (74 to 88) 73% (67 to 78) 67% (62 to 72)
 Ferreira et al. (2014)14 IS 63%-97% 67%-92% 82%-95%

22%-80%

 Rosa et al. (2013)13 84% (81 to 85) 79% (77 to 81) NR NR
 Bloudek et al. (2011)18 80% (73 to 85) 82% (74 to 88) 73% (67 to 78) 67% (62 to 72)
 Formichi et al. (2006)19 NR NR 55%-100% 80%-100%
tTau     
 Ferreira et al. (2014)14 SR 82% (76 to 87) 90% (86 to 93) 73%-91%

75%-98%

 Ferreira et al. (2014)14 IS 61%-91% 53%-97% 61%-92% 40%-93%
 Bloudek et al. (2011)18 82% (76 to 87) 90% (86 to 93) 78% (72 to 83) 75% (68 to 81)
 Formichi et al. (2006)19  NR NR 52%-100% 50%-100%
pTau    
 Ferreira et al. (2014)14 SR 78%-80% 83%-88% 72%-88% 78%-83%
 Ferreira et al. (2014)14 IS 61%-89% 37%-92% 77%-88% 56%-88%
 Bloudek et al. (2011)18 80% (70 to 87) 83% (75 to 88) 79% (72 to 84) 80% (71 to 86)
 Formichi et al. (2006)19  NR NR 37%-100% 80%-100%

Values in parentheses are 95% confidence intervals unless otherwise noted.  
Aβ42: amyloid-β peptide 1-42; CSF: cerebrospinal fluid; IS: individual studies; NR: not reported; pTau: phosphorylated tau protein; SR: systematic review; tTau: total tau protein.
aOr unspecified. 

In a 2006 review of studies using clinical diagnosis as the criterion standard, Formichi et al. identified studies examining diagnostic accuracy of the following CSF markers for AD: tTau (41 studies; 2287 AD patients, 1384 controls; sensitivity, 52%-100%; specificity, 50%-100%), pTau (12 studies; 760 AD patients, 396 controls; sensitivity, 37%-100%; specificity, 80%-100%), and Aβ42 (14 studies; 688 AD patients, 477 controls; sensitivity, 55%-100%; specificity, 80%-100%).19 Although primarily a descriptive review, test accuracies varied widely and only 1 study included a majority of autopsy-confirmed AD diagnoses.

As noted, for patients with clinically diagnosed AD, some have suggested that the tau/Aβ42 ratio is a more accurate predictor than either marker alone. For example, using optimal cutoffs, de Jong et al (2006) reported sensitivity and specificity of 95% and 90% in a sample with clinically diagnosed AD (n=61) and vascular dementia (VaD) (n=61).20 In contrast, Le Bastard et al (2007) found the pTau/Aβ42 ratio lacked specificity to distinguish AD from VaD in a sample of 85 patients (VaD (n=64), AD (n=21); 76/85 autopsy-confirmed diagnoses); specificity was 52% and sensitivity ranged from 91% to 95%.21

CSF Aβ42 level normalized to CSF Aβ40 (i.e., the Aβ42/Aβ40 ratio) is being investigated as a marker for patients with uncertain clinical diagnosis. Because Aβ40 is not incorporated into amyloid plaques, CSF levels are more stable than those of Aβ42. Sauvee et al. (2014) examined the Aβ42/Aβ40 ratio in 122 patients with atypical dementia who had discordant CSF biomarker results (i.e., tau, pTau, Aβ42).22 Using 0.05 as the ratio threshold, biologic profiles were clarified in 72 (59%) of 122 patients with the addition of the Aβ42/Aβ40 ratio. However, of 35 patients diagnosed with AD by biologic profile, 9 (26%) did not meet clinical criteria for AD or mixed dementia. Janelidze et al. (2016) also found that the Aβ42/Aβ40 ratio was significantly better than Aβ42 alone in detecting brain amyloid deposition in prodromal AD and in differentiating AD dementia from non-AD dementias across 3 different immunoassays and 3 patient cohorts.23

Kahle et al. (2000) reported on the diagnostic potential of CSF levels of tTau and neural thread protein in a group of 35 patients with dementia (30 with probable or definite AD), 5 patients with dementia with Lewy bodies, 29 patients with Parkinson's disease, and 16 elderly healthy control patients.24 Levels of both tau and neural thread protein were elevated in patients with AD compared with controls; sensitivity and specificity were 63% and 93%, respectively, for tau, and 70% and 80%, respectively, for neural thread protein.

Section Summary: Clinical Validity of Cerebrospinal Fluid Marker Testing for Diagnosis of AD
Several studies have examined the diagnostic performance of CSF biomarkers for distinguishing probable AD from nondemented controls and from patients with other types of dementia. The range of reported sensitivities and specificities is broad compared to clinical diagnosis reference standard; in systematic reviews with meta-analyses, sensitivity and specificity ranged from 80% to 82% and 82% to 90%, respectively, for differentiating AD from nondemented controls, and 73% and 67%, respectively, for differentiating AD from other dementias. Positive and negative likelihood ratios were 2 to 8 and 0.2 to 0.4, respectively, in either setting. There is limited evidence examining incremental diagnostic accuracy of CSF biomarkers for AD diagnosis employing autopsy as a criterion standard. Cutoffs for positive diagnosis are not standardized. Current evidence does not demonstrate improvement over a clinical diagnosis.

Prognosis for Progression of MCI
Studies have evaluated the prognostic value of markers for progression of MCI and conversion to clinically manifest AD.

Ritchie et al. (2014) published a Cochrane review of CSF amyloid-β protein (primarily Aβ42) for detecting which patients with MCI would progress to AD or other dementias.25 Literature was searched in December 2012, and 14 prospective or retrospective cohort studies of AD were included (1,349 patients with MCI). Studies that enrolled patients younger than 50 years of age or with less than 2 years of follow-up were excluded. Risk of bias was moderate to high in most studies. AD, diagnosed by clinical criteria, developed in 436 (32%) of 1,349 patients. Sensitivity ranged from 36% to 100%, and specificity from 29% to 91%. Due to heterogeneity of thresholds used, summary sensitivity and specificity were not calculated. However, a summary ROC curve was generated using the median specificity of 64%; pooled sensitivity was 81% (95% CI, 72% to 87%). Positive and negative likelihood ratios were 2.2 (95% CI, 2.0 to 2.5) and 0.31 (95% CI, 0.21 to 0.48), respectively. Analysis of the pre- and post-test probabilities of conversion to AD among patients with MCI in primary and secondary care settings showed little incremental value of Aβ42 testing in either setting.

The 2014 meta-review of systematic reviews by Ferriera et al. (previously discussed) included studies of CSF biomarkers for differentiating patients with MCI who progress to AD from those who do not.14 In systematic reviews with meta-analyses, sensitivity and specificity of Aβ42 were 67% (95% CI, 59% to 75%) and 71% (95% CI, 65% to 78%), respectively; for tTau, 82% (95% CI, 76% to 86%) and 70% (95% CI, 65% to 85%), respectively; and for pTau, 81% (95% CI, 69% to 91%) and 65% to 76%, respectively. Positive and negative likelihood ratios for all 3 tests ranged from 2 to 3 and from 0.3 to 0.5, respectively.

In 2016, Olsson et al. performed a comprehensive systematic review and meta-analysis of 231 articles including 15,699 patients with AD and 13,018 controls, published between 1984 and 2014, describing both diagnostic and prognostic performance of CSF biomarkers.26 Five articles were classified as high quality and 226 as medium quality; only studies with autopsy confirmation were eligible to be scored as high quality. Diagnostic and prognostic accuracy were not reported due to large variation in cutoffs for positivity. Instead, biomarker performance was summarized using the ratio of biomarker concentration in patients with AD and controls (ie, fold change) or the ratio of biomarker concentration in those with MCI due to AD and those with stable MCI who had no further cognitive decline during 2 years of follow-up. A fold change ratio above 1 indicates that the concentration of the biomarker is higher in the AD population than in the control population, and a ratio below 1 indicates the concentration is higher in the control population than in the AD population. Summary fold change was calculated with random-effects meta-analysis. CSF tTau, pTau, and Aβ42 levels were consistently and strongly associated with AD diagnosis: CSF tTau average ratio was 2.54 (95% CI, 2.44 to 2.64); pTau average ratio was 1.88 (95% CI, 1.79 to 1.97); and Aβ42 average ratio was 0.56 (95% CI, 0.55 to 0.58). All 3 biomarkers were also able to differentiate between cohorts with MCI due to AD and those with stable MCI: Aβ42 average ratio was 0.67 (95% CI, 0.63 to 0.73); pTau average ratio was 1.72 (95% CI, 1.46 to 2.02); and tTau average ratio was 1.76 (95% CI, 1.64 to 1.89).

Section Summary: Clinical Validity of Cerebrospinal Fluid Marker Testing for Prognosis for Progression of MCI
The evidence suggests that biomarker testing may identify increased risk of conversion from MCI to AD. Studies primarily include clinical diagnosis as a reference standard and varying cutoffs for predicting conversion. CSF biomarkers added little to no incremental value over neuropsychological testing or imaging.

Clinical Utility
Possible clinical uses of CSF biomarker testing could include confirming the diagnosis of AD to begin medications at an earlier stage, or ruling out AD, which could lead to further diagnostic testing to determine the etiology of dementia and/or avoidance of anti-Alzheimer medications that would be unnecessary.

No trials have been identified that reported health outcomes after CSF biomarker testing, thus there is no direct evidence for clinical utility. Decision models can provide indirect evidence of utility if the likelihood of benefits and consequence are estimable. To evaluate the benefits and consequences of CSF biomarker interventions, models would need to describe disease progression, resources use, and quality of life. Such estimates are scarce and highly variable.

Although not without controversy because of modest efficacy, cholinesterase inhibitors are used to treat mild-to-moderate AD.27,28 Memantine, an N-methyl-D-aspartate receptor antagonist, appears to provide a small benefit in treating symptoms in those with moderate-to-advanced disease.27,29 Neither cholinesterase inhibitors nor memantine is disease-modifying.

Given available therapies, in principle, more accurate diagnosis might allow targeting treatment to those most likely to benefit. However, clinical trial entry criteria and benefit have been based on clinical diagnosis. There is less evidence to support use of cholinesterase inhibitors in other dementias, but they are still frequently used to treat cognitive symptoms. While the possibility that more accurate differential diagnosis may lead to improved outcomes is plausible, it is not based on current evidence. Pharmacologic interventions for MCI have not demonstrated benefit in reducing progression to AD.30-33 The indirect chain of clinical utility is incomplete.

Section Summary: Cerebrospinal Fluid Marker Testing
The analytic validity of CSF biomarker measurement in AD is limited by variability between laboratories and assay methods. Most clinical validity studies of both diagnosis and prognosis use select patient samples and define optimal test cutoffs without validation. There is no evidence that improved diagnosis or prognosis leads to improved health outcomes or quality of life.

URINARY MARKER TESTING
Analytic Validity
We found 1 publication describing components of analytic validity for a competitive enzyme-linked immunosorbent assay format affinity assay to measure neural thread protein (NTP) in urine samples.34 Seven hundred twenty replicates were assayed at 4 different clinical laboratories by 4 different trained personnel, on 3 different days each, consisting of high, medium, and low NTP urines in 20 replicates each per day. The CVs were reported to vary from 2.3% to 7.1% in high-NTP urine, 1.5% to 8.5% in medium-NTP urine, and 2.5% to 15% in low-NTP urine. Between and within laboratory variation was not given.

Three lots of high-, medium-, and, low-NTP controls were tested in 4 replicates each for 3 days. The CVs varied from 4.3% to 8.6%. Twenty replicates of low-NTP urine samples were spiked with known concentrations of NTP to 18.9, 23.9, 28.9, 33.9, and 38.9 mg/mL; mean recovery was 105.5%.

Clinical Validity
Zhang et al. (2014) conducted a systematic review and meta-analysis of urinary AD-associated neural thread protein for diagnosing AD in patients with suspected AD.35 Nine studies were included (total N=841 patients with probable or possible AD; 37 patients with MCI, 992 non-AD demented or nondemented controls). The reference standard was clinical diagnosis in 8 studies and not described in 1 study. Varying cutoffs for positive diagnosis were used across included studies. Controls were both health volunteers and patients with other dementias. For probable AD, pooled sensitivity and specificity were 89% (95% CI, 86% to 92%) and 90% (95% CI, 88% to 92%), respectively. Pooled positive and negative likelihood ratios were 8.9 (95% CI, 7.1 1 to 11.1) and 0.12 (95% CI, 0.09 to 0.16), respectively.

In a prospective multicenter study conducted at 8 sites, Goodman et al. (2007) enrolled 168 patients with recent referrals to memory clinics.36 The Urinary Neural Thread Protein Test was 91.4% (32/35) sensitive for a diagnosis of probable AD and 90.1% (39/43) specific among healthy patients.

Clinical Utility
As above, there is no direct evidence or indirect chain of evidence to support the clinical utility of urinary markers for diagnosing AD.

Section Summary: Urinary Marker Testing
Limited data on analytic validity of urine NTP markers is available. Studies of clinical validity include both patients with dementia and normal control. Cutpoints for positive diagnosis varied. There is no direct evidence to support improvements in health outcomes and the indirect chain of evidence is incomplete.

SUMMARY OF EVIDENCE
For individuals who have Alzheimer's disease (AD) or mild cognitive impairment (MCI) who receive cerebrospinal fluid (CSF) biomarker testing for AD, the evidence includes systematic reviews, meta-analyses, and case series. Relevant outcomes are test accuracy and validity, symptoms, change in disease status, morbid events, functional outcomes, quality of life, medication use, and resource utilization. The analytic validity of CSF biomarker measurement in AD is limited by variability between laboratories and assay methods. Most clinical validity studies have been derived from select patient samples and defined optimal test cutoffs without validation; thus, the generalizability of results is uncertain. For predicting conversion from MCI to AD, limited evidence has suggested that testing may define increased risk. Whether earlier diagnosis leads to improved health outcomes through delay of AD onset or improved quality of life is unknown. The evidence is insufficient to determine the effects of the technology on health outcomes.

For individuals who have AD or MCI who receive urinary biomarker testing for AD, the evidence includes a systematic review and observational studies. Relevant outcomes are test accuracy and validity, symptoms, change in disease status, morbid events, functional outcomes, quality of life, medication use, and resource utilization. Limited data are available on the analytic validity of urinary biomarker measurement in AD. Clinical validity studies have included normal healthy controls and defined optimal test cutoffs without validation; thus, clinical validity is uncertain. Whether earlier diagnosis leads to improved health outcomes through delay of AD onset or improved quality of life is unknown. The evidence is insufficient to determine the effects of the technology on health outcomes. 

PRACTICE GUIDELINES AND POSITION STATEMENTS
National Institute of Neurological and Communicative Disorders et al.
In 1984, National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) and Alzheimer's Disease and Related Disorders Association (ADRDA) developed clinical criteria for the diagnosis of AD.37 Although evidence to date has used the NINCDS-ADRDA’s AD classification, in 2011, the National Institute on Aging and the Alzheimer’s Association workgroup revised diagnostic criteria for dementia due to AD.15

In the 1984 guidelines, diagnostic categories were defined as follows.

Possible Alzheimer's Disease
Clinical diagnosis of possible AD:

  1. May be made on the basis of the dementia syndrome in the absence of other neurological, psychiatric, or systemic disorders sufficient to cause dementia, and in the presence of variations in the onset, the presentation, or the clinical course.
  2. May be made in the presence of a second systemic or brain disorder sufficient to produce dementia, which is not considered to be the cause of the dementia.
  3. Should be used in research studies when a single gradually progressive severe cognitive deficit is identified in the absence of other identifiable cause.

Probable Alzheimer's Disease
Criteria for the clinical diagnosis of probable AD included:

  1. Dementia, established by clinical examination and documented by the Mini-Mental State Examination, the Blessed Dementia Scale, or some similar examination and confirmed by neuropsychological tests;
  2. Deficits in 2 or more areas of cognition;
  3. Progressive worsening of memory and other cognitive functions;
  4. No disturbance of consciousness;
  5. Onset between ages 40 and 90 years, most often after the age of 65 years; and
  6. Absence of systemic disorders or other brain diseases that in and of themselves could account for the progressive deficits in memory and cognition.

The diagnosis of probable AD is supported by:

  1. Progressive deterioration of specific cognitive functions such as language (aphasia), motor skills (apraxia), and perception (agnosia);
  2. Impaired activities of daily living and altered patterns of behavior;
  3. Family history of similar disorders, particularly if confirmed neuropathologically; and
  4. Laboratory results: normal lumbar puncture as evaluated by standard techniques, normal pattern or nonspecific changes in the electroencephalogram (EEG), and evidence of cerebral atrophy on computed tomography (CT) scanning with progression documented by serial observation.

Other clinical features consistent with the diagnosis of probable AD, after exclusion of causes of dementia other than AD, include

  1. Plateaus in the course of progression of the illness;
  2. Associated symptoms of depression, insomnia, incontinence, delusions, illusions, hallucinations, sexual disorders, weight loss, and catastrophic verbal, emotional, or physical outbursts;
  3. Other neurological abnormalities in some patients, especially with more advanced disease and including motor signs such as increased muscle tone, myoclonus, or gait disorder; and
  4. Seizures in advanced disease CT normal for age.

Features that make the diagnosis of probable AD uncertain or unlikely include:

  1. Sudden apoplectic onset;
  2. Focal neurological findings such as hemiparesis, sensory loss, visual field deficits, and incoordination early in the course of the illness; and
  3. Seizures or gait disturbances at the onset or very early in the course of the illness.

Definite Alzheimer's Disease
Criteria for diagnosis of definite AD are:

  1. Clinical criteria for probable Alzheimer's disease; AND 
  2. Histopathologic evidence obtained from a biopsy or autopsy.

National Institute on Aging and the Alzheimer’s Association
As of 2011, probable AD was defined by the National Institute on Aging and the Alzheimer’s Association workgroup using the following diagnostic criteria15:

"Meets criteria for dementia…and in addition, has the following characteristics:

  1. Insidious onset. Symptoms have a gradual onset over months to years, not sudden over hours or days;
  2. Clear-cut history of worsening of cognition by report or observation; and
  3. The initial and most prominent cognitive deficits are evident on history and examination in one of the following categories.
    • Amnestic presentation: It is the most common syndromic presentation of AD dementia. The deficits should include impairment in learning and recall of recently learned information. There should also be evidence of cognitive dysfunction in at least one other cognitive domain, as defined earlier in the text.
    • Nonamnestic presentations: Language presentation: The most prominent deficits are in word-finding, but deficits in other cognitive domains should be present. Visuospatial presentation: The most prominent deficits are in spatial cognition, including object agnosia, impaired face recognition, simultanagnosia, and alexia. Deficits in other cognitive domains should be present. Executive dysfunction: The most prominent deficits are impaired reasoning, judgment, and problem solving. Deficits in other cognitive domains should be present.
  4. The diagnosis of probable AD dementia should not be applied when there is evidence of:
    • Substantial concomitant cerebrovascular disease, defined by a history of a stroke temporally related to the onset or worsening of cognitive impairment; or the presence of multiple or extensive infarcts or severe white matter hyperintensity burden; or
    • Core features of dementia with Lewy bodies other than dementia itself; or
    • Prominent features of behavioral variant frontotemporal dementia; or
    • Prominent features of semantic variant primary progressive aphasia or nonfluent/agrammatic variant primary progressive aphasia; or
    • Evidence for another concurrent, active neurological disease, or a non-neurological medical comorbidity or use of medication that could have a substantial effect on cognition."

All probable AD by NINCDS-ADRDA criteria are subsumed in the revised probable AD criteria. Revised criteria include a category of "Probable AD dementia with increased level of certainty" due to documented decline or having a causative AD genetic mutation. Additionally, a category "Probable AD dementia with evidence of the AD pathophysiological process" has been added. Evidence of the AD pathophysiologic process is supported by detection of low cerebrospinal fluid (CSF) amyloid-β peptide 1-42 (Aβ42), positive positron emission tomography (PET) amyloid imaging, or elevated CSF tau, and decreased 18-F fluorodeoxyglucose uptake on PET in the temporoparietal cortex with accompanying atrophy by magnetic resonance imaging in relevant structures. Detection of the "pathophysiological process" is further divided by when in the disease natural history markers are expected to be detectable.

Note on Revised AD Criteria and Biomarkers
The biomarkers considered in this evidence review included in a category among revisions to the 2011 updated AD diagnostic criteria, "probable AD dementia with evidence of the AD pathophysiological process."15 However, the diagnostic criteria workgroup noted that

"we do not advocate the use of AD biomarker tests for routine diagnostic purposes at the present time. There are several reasons for this limitation: 1) the core clinical criteria provide very good diagnostic accuracy and utility in most patients; 2) more research needs to be done to ensure that criteria that include the use of biomarkers have been appropriately designed, 3) there is limited standardization of biomarkers from one locale to another, and 4) access to biomarkers is limited to varying degrees in community settings. Presently, the use of biomarkers to enhance certainty of AD pathophysiological process may be useful in 3 circumstances: investigational studies, clinical trials, and as optional clinical tools for use where available and when deemed appropriate by the clinician."15  

Alzheimer’s Association
In 2009, the Alzheimer’s Association (AA) initiated a quality control program for CSF markers, noting that "Measurements of CSF AD biomarkers show large between laboratory variability, likely caused by factors related to analytical procedures and the analytical kits. Standardization of laboratory procedures and efforts by kit vendors to increase kit performance might lower variability, and will likely increase the usefulness of CSF AD biomarkers."

18 In 2012, the Alzheimer's Biomarkers Standardization Initiative published consensus recommendations for standardization of preanalytical aspects (eg, fasting, tube types, centrifugation, storage time, temperature) of CSF biomarker testing.38 

In 2013, AA published recommendations for operationalizing the detection of cognitive impairment during the Medicare annual wellness visit in primary care settings.39 The recommended algorithm for cognitive assessment was based on "current validated tools and commonly used rule-out assessments." Guidelines noted that use of biomarkers (eg, CSF tau and β-amyloid proteins) "was not considered as these measures are not currently approved or widely available for clinical use."  

The 4th Canadian Consensus Conference on Diagnosis and Treatment of Dementia
The 4th Canadian Consensus Conference on Diagnosis and Treatment of Dementia published updated evidence-based consensus recommendations in 2012.40,41 There was consensus that plasma Aβ42 measurement is unreliable and is not recommended for clinical practice. There was lack of consensus for measurement of CSF Aβ42 and tau levels in patients with atypical dementia. Conference participants concluded that "for now, measurement of CSF AB1-42 and tau have no clinical utility in Canada, although they are part of research protocols in observational and therapeutic studies."  

European Federation of Neurological Societies and European Neurological Society
In 2012, European Federation of Neurological Societies and European Neurological Society published updated evidence-based consensus guidelines on the diagnosis and management of disorders associated with dementia.42 Included was a level B recommendation (probably effective based on class 3 [unblinded] evidence) that CSF Aβ42/tau/pTau assessment helps to differentiate AD.  

U.S. PREVENTIVE SERVICES TASK FORCE RECOMMENDATIONS
Not applicable.

ONGOING AND UNPUBLISHED CLINICAL TRIALS
A search of ClinicalTrials.gov in November 2016 did not identify any ongoing or unpublished trials that would likely influence this review. 

References:

  1. Albert MS, DeKosky ST, Dickson D, et al. The diagnosis of mild cognitive impairment due to Alzheimer's disease: recommendations from the National Institute on Aging-Alzheimer's Association workgroups on diagnostic guidelines for Alzheimer's disease. Alzheimers Dement. May 2011;7(3):270-279. PMID 21514249
  2. Hyman BT, Phelps CH, Beach TG, et al. National Institute on Aging-Alzheimer's Association guidelines for the neuropathologic assessment of Alzheimer's disease. Alzheimers Dement. Jan 2012;8(1):1-13. PMID 22265587
  3. Galasko D, Clark C, Chang L, et al. Assessment of CSF levels of tau protein in mildly demented patients with Alzheimer's disease. Neurology. Mar 1997;48(3):632-635. PMID 9065538
  4. Motter R, Vigo-Pelfrey C, Kholodenko D, et al. Reduction of beta-amyloid peptide42 in the cerebrospinal fluid of patients with Alzheimer's disease. Ann Neurol. Oct 1995;38(4):643-648. PMID 7574461
  5. Zhang J, Peng M, Jia J. Plasma amyloid-beta oligomers and soluble tumor necrosis factor receptors as potential biomarkers of AD. Curr Alzheimer Res. May 2014;11(4):325-331. PMID 24635842 
  6. Maddalena A, Papassotiropoulos A, Muller-Tillmanns B, et al. Biochemical diagnosis of Alzheimer disease by measuring the cerebrospinal fluid ratio of phosphorylated tau protein to beta-amyloid peptide42. Arch Neurol. Sep 2003;60(9):1202-1206. PMID 12975284
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  8. Mattsson N, Andreasson U, Persson S, et al. The Alzheimer's Association external quality control program for cerebrospinal fluid biomarkers. Alzheimers Dement. Jul 2011;7(4):386-395 e386. PMID 21784349
  9. Shaw LM, Vanderstichele H, Knapik-Czajka M, et al. Qualification of the analytical and clinical performance of CSF biomarker analyses in ADNI. Acta Neuropathol. May 2011;121(5):597-609. PMID 21311900
  10. Lewczuk P, Beck G, Ganslandt O, et al. International quality control survey of neurochemical dementia diagnostics. Neurosci Lett. Nov 27 2006;409(1):1-4. PMID 17045397
  11. Verwey NA, van der Flier WM, Blennow K, et al. A worldwide multicentre comparison of assays for cerebrospinal fluid biomarkers in Alzheimer's disease. Ann Clin Biochem. May 2009;46(Pt 3):235-240. PMID 19342441
  12. Monge-Argilés JA, Munoz-Ruiz C, Sanchez-Paya J, et al. Comparison of two analytical platforms for CSF biomarkers of Alzheimer's disease. Biomed Res Int. 2014;2014:765130. PMID 24971348
  13. Rosa MI, Perucchi J, Medeiros LR, et al. Accuracy of cerebrospinal fluid Abeta(1-42) for Alzheimer's disease diagnosis: a systematic review and meta-analysis. J Alzheimers Dis. 2014;40(2):443-454. PMID 24448789
  14. Ferreira D, Perestelo-Perez L, Westman E, et al. Meta-review of CSF core biomarkers in Alzheimer's disease: the state-of-the-art after the new revised diagnostic criteria. Front Aging Neurosci. 2014;6:47. PMID 24715863
  15. McKhann GM, Knopman DS, Chertkow H, et al. The diagnosis of dementia due to Alzheimer's disease: recommendations from the National Institute on Aging-Alzheimer's Association workgroups on diagnostic guidelines for Alzheimer's disease. Alzheimers Dement. May 2011;7(3):263-269. PMID 21514250
  16. van Harten AC, Kester MI, Visser PJ, et al. Tau and p-tau as CSF biomarkers in dementia: a meta-analysis. Clin Chem Lab Med. Mar 2011;49(3):353-366. PMID 21342021
  17. Cure S, Abrams K, Belger M, et al. Systematic literature review and meta-analysis of diagnostic test accuracy in Alzheimer's disease and other dementia using autopsy as standard of truth. J Alzheimers Dis. May 19 2014;42(1):169-182. PMID 24840572
  18. Bloudek LM, Spackman DE, Blankenburg M, et al. Review and meta-analysis of biomarkers and diagnostic imaging in Alzheimer's disease. J Alzheimers Dis. 2011;26(4):627-645. PMID 21694448
  19. Formichi P, Battisti C, Radi E, et al. Cerebrospinal fluid tau, A beta, and phosphorylated tau protein for the diagnosis of Alzheimer's disease. J Cell Physiol. Jul 2006;208(1):39-46. PMID 16447254
  20. de Jong D, Jansen RW, Kremer BP, et al. Cerebrospinal fluid amyloid beta42/phosphorylated tau ratio discriminates between Alzheimer's disease and vascular dementia. J Gerontol A Biol Sci Med Sci. Jul 2006;61(7):755-758. PMID 16870640
  21. Le Bastard N, Van Buggenhout M, De Leenheir E, et al. LOW specificity limits the use of the cerebrospinal fluid AB1-42/P-TAU181P ratio to discriminate Alzheimer's disease from vascular dementia. J Gerontol A Biol Sci Med Sci. Aug 2007;62(8):923-924; author reply 924-925. PMID 17702886
  22. Sauvee M, DidierLaurent G, Latarche C, et al. Additional use of abeta42/abeta40 ratio with cerebrospinal fluid biomarkers p-tau and abeta42 increases the level of evidence of Alzheimer's disease pathophysiological process in routine practice. J Alzheimers Dis. 2014;41(2):377-386. PMID 24614902
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  24. Kahle PJ, Jakowec M, Teipel SJ, et al. Combined assessment of tau and neuronal thread protein in Alzheimer's disease CSF. Neurology. Apr 11 2000;54(7):1498-1504. PMID 10751266
  25. Ritchie C, Smailagic N, Noel-Storr AH, et al. Plasma and cerebrospinal fluid amyloid beta for the diagnosis of Alzheimer's disease dementia and other dementias in people with mild cognitive impairment (MCI). Cochrane Database Syst Rev. 2014;6:CD008782. PMID 24913723
  26. Olsson B, Lautner R, Andreasson U, et al. CSF and blood biomarkers for the diagnosis of Alzheimer's disease: a systematic review and meta-analysis. Lancet Neurol. Jun 2016;15(7):673-684. PMID 27068280
  27. Raina P, Santaguida P, Ismaila A, et al. Effectiveness of cholinesterase inhibitors and memantine for treating dementia: evidence review for a clinical practice guideline. Ann Intern Med. Mar 4 2008;148(5):379-397. PMID 18316756
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Coding Section

Codes Number Description
CPT   See Policy Guidelines
ICD-9 Procedure    
ICD-9 Diagnosis   Investigational for all relevant diagnoses
HCPCS    
ICD-10-CM (effective 10/01/15)   Investigational for all relevant diagnoses
  F03 Unspecified dementia
  G30.0-G30.9 Alzheimer disease code range
  G31.1 Senile degeneration of brain, not elsewhere classified
  R41.0 Disorientation, unspecified
  R41.81 Age-related cognitive decline
  Z13.858 Encounter for screening for other nervous system disorders
ICD-10-PCS (effective 10/01/15)   Not applicable. ICD-10-PCS codes are only used for inpatient services. There are no ICD procedure codes for laboratory tests.
Type of Service Pathology/Laboratory  
Place of Service Physician's Office  

Procedure and diagnosis codes on Medical Policy documents are included only as a general reference tool for each policy. They may not be all-inclusive.  

This medical policy was developed through consideration of peer-reviewed medical literature generally recognized by the relevant medical community, U.S. FDA approval status, nationally accepted standards of medical practice and accepted standards of medical practice in this community, Blue Cross and Blue Shield Association technology assessment program (TEC) and other non-affiliated technology evaluation centers, reference to federal regulations, other plan medical policies and accredited national guidelines. 

"Current Procedural Terminology© American Medical Association.  All Rights Reserved"  

History From 2014 Forward     

10/29/2018 

Annual review, no change to policy intent. 

11/06/2017 

Annual review, no change to policy intent. Updating rationale and references. 

04/25/2017 

Updated category to Laboratory 

07/05/2016 

Annual review, no change to policy intent. Updating background, description, regulatory status, rationale and references. 

07/20/2015 

Annual review, no change to policy intent. Updated background, description, rationale and references. Added guidelines, regulatory status and coding. 

07/08/2014

Annual review. Updated background, description, rationale and references. Added related policies. No change to policy intent.


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