Background

Crysvita® (burosumab-twza) is a monoclonal antibody that blocks fibroblast growth factor 23 (FGF23), a hormone involved in phosphate regulation. Excess FGF23 activity results in renal phosphate wasting, chronic hypophosphatemia, impaired bone mineralization, rickets, osteomalacia, fractures, skeletal deformities, and bone pain. Crysvita increases serum phosphorus levels and improves bone mineralization by targeting the underlying disease mechanism.

Crysvita is FDA-approved for the treatment of X-linked hypophosphatemia (XLH) in adult and pediatric patients 6 months of age and older and for FGF23-related hypophosphatemia in tumor-induced osteomalacia (TIO) associated with phosphaturic mesenchymal tumors that cannot be curatively resected or localized in adult and pediatric patients 2 years of age and older. Prior to initiating therapy, oral phosphate and active vitamin D analogs should be discontinued.

Policy Criteria

Initial Authorization Criteria

Linked Hypophosphatemia (XLH)

Coverage of Crysvita may be considered medically necessary when all of the following criteria are met:

X-linked hypophosphatemia (XLH)

1. Diagnosis of X-linked hypophosphatemia (XLH)
2. Prescribed by or in consultation with one of the following:
   1. Endocrinologist
   2. Specialist experienced in the treatment of inborn errors of metabolism
3. One of the following:
   1. Patient is 6 months to 17 years of age
   2. Both of the following:
      1. Patient is 18 years of age or older
      2. Patient is a candidate for pharmacologic therapy by meeting at least one of the following:
         1. Spontaneous insufficiency fractures
         2. Pending orthopedic procedures (e.g., joint replacement)
         3. Biochemical evidence of osteomalacia (elevated serum alkaline phosphatase)
         4. Disabling skeletal pain
4. Trial and failure, contraindication, or intolerance to both of the following:
   1. Phosphate supplementation
   2. Vitamin D analog-based therapy (e.g., calcitriol, paricalcitol, doxercalciferol)

Tumor-Induced Osteomalacia (TIO)

Coverage of Crysvita may be considered medically necessary when all of the following criteria are met:

1. Diagnosis of FGF23-related hypophosphatemia in Tumor-Induced Osteomalacia (TIO)
2. Tumor cannot be curatively resected or localized.
3. Patient is 2 years of age or older.
4. Trial and failure, contraindication, or intolerance to both of the following:
   1. Phosphate supplementation
   2. Vitamin D analog-based therapy (e.g., calcitriol, paricalcitol, doxercalciferol)
5. Prescribed by or in consultation with one of the following:
   1. Oncologist
   2. Endocrinologist

Authorization Duration

Initial approval may be granted for up to 12 months.

Reauthorization Criteria

X-Linked Hypophosphatemia (XLH)

Continued coverage may be considered medically necessary when patient demonstrates a positive clinical response to therapy, including one or more of the following:

• Improvement in rickets
• Improvement in serum phosphorus levels
• Improvement in Radiographic Global Impression of Change (RGI-C) scores
• Stabilization or improvement of skeletal manifestations

Tumor-Induced Osteomalacia (TIO)

Continued coverage may be considered medically necessary when patient demonstrates a positive clinical response to therapy, including one or more of the following:

• Increased serum phosphorus levels
• Improvement in osteoid thickness
• Improvement in osteoid surface
• Improvement in osteoid volume
• Improvement in mineralization lag time
• Improvement documented by bone biopsy

Authorization Duration

Reauthorization may be granted for up to 12 months.

References

1. CRYSVITA® (burosumab-twza) injection Prescribing Information. Kyowa Kirin, Inc.. Revised 2026.
2. CRYSVITA® (burosumab-twza) injection Prescribing Information. U.S. Food and Drug Administration. Revised 2025.
3. CRYSVITA® Full Prescribing Information. Kyowa Kirin.
4. CRYSVITA (burosumab-twza) Prescribing Information: Treatment for XLH and TIO.
5. Crysvita: Package Insert / Prescribing Information.

Coding Section

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, technology assessment program (TEC) and other non-affiliated technology evaluation centers, reference to federal regulations, other plan medical policies, and accredited national guidelines.

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