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RTM Testing of Homocysteine Metabolism-Related Conditions
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This policy governs coverage and reimbursement criteria for testing related to homocysteine metabolism (including newborn screening, plasma total homocysteine, and related biochemical and genetic testing) for Oscar Health members. It applies to providers submitting claims for these diagnostic tests and to determination of medical necessity and authorization.
No material clinical or coverage changes in this revision.
Coverage Criteria and Indications
Covered Indications
Covered when ANY of the following are met
Supports newborn screening coverage
Covered as part of newborn screening programs
Covered as newborn screening target
Actionable follow-up testing after positive screen
Covers diagnostic and monitoring tHcy testing in adults
Covered indications and diagnostic pathway
Coverage-aligned clinical indications and confirmatory testing described in guidelines:
Obtain plasma and urine samples for MMA, methionine, folate and vitamin B12 before treatment if tHcy is high.
Two-tier newborn screening strategy recommended by guidelines to increase specificity
Enzymatic testing in fibroblasts is gold standard but may not be available; molecular testing is recommended when enzyme testing is not available or to confirm diagnosis.
Plasma free homocysteine testing does not meet criteria for coverage under this policy. The policy explicitly states that plasma free homocysteine testing is not covered and should not be used as a standalone diagnostic test.
Guideline recommendations indicate that total homocysteine (tHcy) is the frontline biochemical test and that measuring free homocysteine instead of total homocysteine is strongly not recommended. Therefore, plasma free homocysteine measurement is not indicated as a replacement for tHcy in diagnostic workflows.
Within the cited evidence and reference materials there are no additional explicit coverage exclusions listed beyond those already stated for plasma free homocysteine; the references provide supporting studies and validation methods for total homocysteine testing.
Separate measurement of plasma free homocysteine is unnecessary because total homocysteine (tHcy) already includes all biochemical forms of homocysteine. The document notes that free Hcy comprises only about 15–25% of tHcy and that separate free Hcy testing adds no diagnostic value and is not required.
The provided reference list and evidence summaries do not contain any explicit statements labeling other services as not medically necessary; the focus of the cited literature is on supporting tHcy as the recommended assay and on methodological validation.
Specific Covered Indications and Diagnostic Confirmation
Genetic testing to detect biallelic pathogenic variants in CBS to substantiate a diagnosis of classic homocystinuria.
Detection of biallelic pathogenic CBS variants substantiates diagnosis and informs pyridoxine-responsiveness phenotype assessment.
Confirmatory testing for CBS deficiency (suspected homocystinuria) following biochemical evidence (elevated tHcy ± Met).
Obtain plasma and urine for MMA, methionine, folate and B12 prior to treatment when tHcy is high.
Enzymatic testing in fibroblasts is the gold standard but may not be available in the USA; molecular testing is recommended for confirmation and for carrier/prenatal testing.
Genetic testing for MTHFR and other remethylation pathway genes in cases with clinical features where identification changes management.
Identification of treatable remethylation defects can guide vitamin-based therapies.
MTHFR polymorphism results should be interpreted with clinical context; alone they have limited contribution to tHcy variance.
Newborn screening and diagnostic evaluation for homocystinurias, remethylation disorders, and elevated methionine/homocysteine
Guideline sources (ACMG, RUSP, E-HOD) support two-tier newborn screening strategies to improve specificity and sensitivity.
Monitoring targets and frequencies are guideline-directed; use proposed tHcy targets for pyridoxine-responsive and -unresponsive patients as appropriate.
Tests and Indications Not Supported
Separate plasma free homocysteine testing is not covered because it is unnecessary for diagnosis—the policy and supporting evidence emphasize tHcy as the diagnostic analyte. In addition, enzymatic testing for cystathionine β-synthase (CBS) deficiency (the historical gold standard in fibroblasts) is noted as no longer available in the USA, further underscoring reliance on tHcy and molecular testing pathways.
Measurement of plasma free homocysteine as a substitute for total homocysteine is not supported. E-HOD guidance specifically recommends against using free Hcy in place of tHcy because free Hcy is detectable only at very high tHcy concentrations and is not sensitive or reproducible.
The evidence and reference sections do not enumerate any other specific laboratory tests or clinical indications that are explicitly excluded from coverage beyond the statements about plasma free homocysteine.
Procedure Codes, References, and Reference Values
| K100987 | FDA Invader MTHFR 677 510(k) Summary (cited) |
| K100496 | FDA 510(k) submission (link cited) |
| K093974 | FDA eSensor Thrombophilia Risk Test on XT-8 System 510(k) (cited) |
| K070597 | FDA Nanosphere 510(k) Summary (cited) |
Provider Responsibilities and Operational Guidance
Confirm benefit coverage and authorization requirements
Services must meet authorization and medical necessity guidelines; application of the criteria depends on the member's benefit coverage at time of request and may be affected by Medicare/Medicaid specifications. Providers should confirm benefit/authorization requirements before ordering testing.
510(k) submissions cited — no payer-specific authorization tied to device status
The policy cites FDA 510(k) summaries for referenced assays and devices (e.g., Invader MTHFR 677/1298 and other 510(k) submissions) but does not impose additional payer-specific prior authorization requirements based on device 510(k) status.
- FDA Invader MTHFR 677 510(k) Summary (K100987)
- FDA Invader MTHFR 1298 510(k) Summary (cited)
- Additional 510(k) summaries cited: K100496, K093974, K070597
Follow guideline-recommended testing workflow
Follow clinical guidelines cited in this policy: measure plasma total homocysteine (tHcy) as the frontline biochemical test for suspected remethylation or CBS deficiency and use two‑tier newborn screening algorithms where applicable. Order genetic confirmation only when indicated by biochemical results or clinical suspicion.
- Measure plasma tHcy as frontline test; centrifuge sample within an hour and keep cold or frozen until analysis (E‑HOD).
- Use Met or Met:Phe as first‑tier in newborn screening and tHcy as a second‑tier to increase specificity (E‑HOD).
- Confirm CBS deficiency by enzyme assay in fibroblasts or by molecular analysis of CBS; molecular testing recommended for confirmation, carrier, and prenatal testing.
No step‑therapy; follow two‑tier newborn screening and monitoring guidance
No formal step‑therapy is specified in this policy. For newborn screening and follow‑up, the guidance recommends a two‑tier algorithm (Met or Met/Phe first‑tier, followed by tHcy second‑tier) and ongoing biochemical monitoring during therapy as clinically indicated.
- Two‑tier newborn screening: Met or Met:Phe first‑tier; if abnormal perform tHcy as second‑tier.
- Monitor tHcy, amino acids, folate and vitamin B12 during therapy with frequency individualized to the patient.
Document clinical and biochemical rationale before molecular testing
Obtain and retain documentation that supports clinical suspicion and biochemical findings before ordering molecular testing; include evidence of elevated tHcy or abnormal newborn screening results when submitting for authorization or claims review.
- Document clinical signs/symptoms prompting testing and biochemical results (tHcy, Met).
- If available, document prior newborn screen results and second‑tier tHcy testing for follow‑up.
Submit accurate documentation and code claims per industry standards
Providers are responsible for accurate claim documentation and must code claims according to industry standard coding guidelines (e.g., CPT, ICD‑10) to support reimbursement and authorization determinations.
- Submit accurate supporting documentation with claims to avoid denial or recoupment.
- Code claims per standard guidelines (CPT, ICD‑10, HCPCS, UB).
Collect pre‑treatment plasma and urine samples for biochemical confirmation
When total homocysteine is high, obtain plasma and urine samples for methylmalonic acid (MMA), methionine, folate and vitamin B12 before initiating treatment to ensure valid diagnostic evaluation.
- Collect plasma and urine for MMA, methionine, folate and B12 prior to treatment when tHcy is elevated.
- Process plasma promptly (centrifuge within one hour and keep cold or frozen until analysis).
Use ACMG ACT sheets/algorithms for newborn screening follow‑up documentation
ACMG newborn screening ACT sheets and algorithms are cited as supporting resources and may inform documentation and follow‑up workflows for newborns with elevated methionine or suspected homocystinurias.
- ACMG Newborn Screening ACT Sheet [Increased Methionine] — Homocystinuria (CBS Deficiency).
- ACMG Methionine Algorithm and related ACT sheets cited in references.
Risk of denial or recoupment for improper coding or lack of authorization
Claims may be denied or recouped if coding/billing guidelines or current reimbursement policies are not followed; services must meet authorization and medical necessity requirements to be payable.
- Failure to follow appropriate coding/billing guidelines may result in claim denial or recoupment.
- Ensure tests meet medical necessity and authorization criteria prior to submission.
Follow applicable government policies when they conflict with this policy
If this policy conflicts with an applicable government policy (e.g., Medicare LCD/NCD or state Medicaid rules), the government policy takes precedence and will be used to make coverage determinations.
- Refer to Medicare and state Medicaid policies when there is a potential conflict.
- Government policies supersede this policy for affected members.
No other authorization or denial rules specified
No additional payer-specific authorization or denial rules are stated in these sections of the policy.
Order molecular genetic testing for confirmation, carrier, and prenatal testing as indicated
Molecular genetic testing is recommended to confirm CBS deficiency, for carrier testing, and for prenatal testing when appropriate; prenatal molecular analysis is preferred in the first trimester if family mutations are known.
- Use molecular testing of CBS (single‑gene or multigene panels) to confirm diagnosis when biochemical evidence supports homocystinuria.
- Prenatal molecular analysis is preferred in first trimester when familial mutations are known; enzyme analysis in cultured amniocytes is an alternative.
Begin with biochemical screening (tHcy) before molecular confirmation when possible
Order biochemical testing (plasma tHcy ± methionine) first when clinical suspicion exists; only proceed to molecular testing when biochemical results support the diagnosis or as indicated for family/prenatal testing.
- Measure plasma tHcy as the frontline test; process and store samples per guidance.
- Proceed to molecular or enzymatic confirmation when tHcy is elevated or newborn screening follow‑up indicates.
Member Eligibility and Applicability
There are no top-level eligibility requirement nodes specified in this policy.
There are no top-level eligibility requirement nodes specified in this policy.
There are no top-level eligibility requirement nodes specified in this policy.
Clinical Background and Scope
Homocystinuria is an inherited metabolic disorder most commonly due to CBS deficiency, leading to accumulation of homocysteine and methionine and causing ocular, skeletal, thrombotic, and neurodevelopmental manifestations. Early detection—including newborn screening—and treatment can prevent or reduce severity. Measurement of total homocysteine (tHcy) in plasma is the primary clinical analyte for diagnosis; methionine measurement can corroborate the diagnosis. Reference thresholds described in the evidence include tHcy <15 µmol/L as normal, newborns with homocystinuria >50 µmol/L, and older untreated individuals often >100 µmol/L.
Key Definitions and Acronyms
Policy Dates and References
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