ModifiedBlue Cross Blue Shield - LouisianaPolicy AHS - M2141

Testing of Homocysteine Metabolism-Related Conditions

Coverage policy for laboratory testing related to homocystinuria and other homocysteine metabolism disorders, including newborn screening, diagnostic, and monitoring tests; applies to Blue Cross and Blue Shield of Louisiana members.

Policy Summary

PayerBlue Cross Blue Shield - Louisiana

PolicyTesting of Homocysteine Metabolism-Related Conditions

Policy CodePolicy AHS - M2141

Change TypeRemoved pyridoxine challengeremoved select genetic criteria and codesCPT cleanup

Effective DateMay 15, 2022

Next Review Date

Key ActionObtain plasma total homocysteine (tHcy) with proper rapid centrifugation and cold storage for diagnostic confirmation and monitoring; collect plasma and urine for MMA, methionine, folate and B12 before treatment if tHcy is high.

SourceLink

POLICY UPDATE CHANGES

Removed CC3, as the pyridoxine (B6) challenge test is a medical procedure, not a laboratory test and as such, is outside the scope of Avalon management.

Removed CPT code 84207.

Removed genetic coverage criteria CC1, CC2, CC3, CC9 and Note 1 and removed genetic CPT codes 81291, 81401, 81406, 81479 in the 05/01/2024 RTM presentation.

coveredNewborn screening

neonate >50 µmol/LtHcy thresholds (key)

>100 µmol/LTypical untreated tHcy

Trek Health ingests and normalizes Transparency in Coverage data and payer policy updates to give provider organizations a clear view of how commercial reimbursement behaves across markets, payers, and services. Our platform transforms raw payer disclosures into structured intelligence that supports contract evaluation, payer negotiations, and service line strategy. By combining market benchmarks with ongoing policy visibility, Trek helps teams identify variability, risk, and opportunity in commercial reimbursement. The result is faster insight, stronger negotiating positions, and more informed financial decisions.

Monitoring target (pyridoxine-responsive)

5 codesProcedure codes listed

Coverage Criteria

inv-01: Covered Indications

Covered when ANY of the following are met:

Newborn screening for homocysteine-related conditions meets coverage criteria when screening for classic homocystinuria due to CBS deficiency by performing quantitative plasma amino acid analysis and/or plasma or urine total homocysteine analysis, or when screening for homocystinuria or hypermethioninemia in dried blood spots.

Includes dried blood spot screening and Met-based screening with second-tier tHcy per guidelines.

Repeat/confirmatory testing after positive screen: When the initial newborn screening methionine result exceeds the laboratory cut-off, a repeat dried blood specimen submitted to the newborn screening program OR a quantitative plasma amino acid analysis and plasma total homocysteine analysis meet coverage criteria.

Used to confirm initial positive newborn screens.

Adult diagnostic and monitoring: For individuals over 18 years of age with suspected homocystinuria due to CBS deficiency and for monitoring therapy in those with confirmed CBS deficiency, plasma total homocysteine (tHcy) testing meets coverage criteria.

Intended for diagnostic confirmation and therapeutic monitoring.

inv-02: Diagnostic, newborn screening, confirmation, and monitoring

Covered when testing aligns with diagnostic and monitoring guidance from E-HOD and related guidelines

Frontline diagnostic testing: Measure total homocysteine (tHcy) in blood as the initial (frontline) test for patients with suspected remethylation disorders or clinical features suggestive of homocystinuria; immunoassays or chromatographic methods are acceptable.

Specimen should be centrifuged within an hour and kept at 4°C or frozen until analysis.

Newborn screening approach: Newborn screening for CBS deficiency and some remethylation disorders using elevated methionine and methionine-to-phenylalanine (Met:Phe) ratio in dried blood spots, with tHcy used as a second-tier marker to increase specificity (Met/tHcy ratio may also be calculated).

Efficacy for some defects (cblD-Hcy, CblE, cblG, MTHFR deficiency) is uncertain.

Confirmatory testing: Confirm CBS deficiency by measuring cystathionine synthase activity in cultured fibroblasts or plasma and/or by mutation analysis of the CBS gene; if one method is inconclusive, perform the other.

Enzyme assay in cultured fibroblasts is the gold standard; molecular testing is recommended for carrier and prenatal testing with specific specimen guidance.

Plasma-based assays generally provide superior analytical performance for most analytes compared with dried blood spot methods; however, dried blood spot sampling demonstrates acceptable stability for total homocysteine (tHcy) and strong correlation with plasma tHcy in some studies. For clinical use, plasma tHcy is the preferred frontline specimen when feasible, while dried blood spot tHcy may be used when plasma processing is not possible.

The policy clarifies that the pyridoxine (B6) challenge test has been removed from the laboratory coverage criteria because it is classified as a medical procedure rather than a laboratory test and therefore is outside the scope of laboratory test management and coverage under this policy.

Separate measurement of free homocysteine is unnecessary for routine diagnostic purposes because total homocysteine (tHcy) includes free plus bound forms. tHcy is the established analyte for diagnosis: normal <15 µmol/L, neonates with homocystinuria typically >50 µmol/L, and untreated older individuals commonly >100 µmol/L.

Measurement of free homocysteine instead of total homocysteine is not recommended because free Hcy is only detectable at high tHcy concentrations (typically above 50–60 µmol/L) and has poor sensitivity and reproducibility. Guideline authors therefore strongly recommend using tHcy as the diagnostic and monitoring analyte rather than free Hcy.

Covered Indications and Use Cases

inv-23: Newborn screening for classic homocystinuria and hypermethioninemia using dried blood spot methionine and/or Met:Phe ratio, with second-tier tHcy as needed. Also covers plasma amino acid analysis and plasma tHcy for confirmation; measurement of plasma tHcy recommended as frontline test in symptomatic individuals.

Newborn screening for classic homocystinuria or hypermethioninemia: Screen newborns using dried blood spot measurement of methionine and/or methionine-to-phenylalanine ratio; use total homocysteine (tHcy) as a second-tier test when indicated to increase specificity.

Met/tHcy ratio calculation and second-tier tHcy recommended per E-HOD guidance.

Confirmatory testing following abnormal newborn screen: When newborn screening methionine exceeds the cut-off, perform a repeat dried blood specimen submission to the newborn screening program OR quantitative plasma amino acid analysis plus plasma total homocysteine analysis for confirmation.

Also acceptable to use plasma amino acid analysis and plasma tHcy to confirm diagnosis of classic homocystinuria.

Plasma tHcy for symptomatic patients:

Coding and Expected Values

Procedure codes listedCPT

82136	Amino acids, 2 to 5 amino acids, quantitative, each specimen
82139	Amino acids, 6 or more amino acids, quantitative, each specimen
82615	Cystine and homocysteine, urine, qualitative
83090	Homocysteine
83921	Organic acid, single, quantitative

Total homocysteine (tHcy) expected values

Neonate with homocystinuria50 to >100 µmol/L

Untreated older individual with homocystinuria>100 µmol/L

Control (normal) tHcy<15 µmol/L

tHcy diagnostic and monitoring thresholds

Detectable plasma free homocysteineOnly detectable at tHcy concentrations above 50–60 µmol/L

Typical untreated CBS patient tHcy>100 µmol/L

Therapeutic monitoring targets

Provider Actions and Operational Notes

Denial Risk

Benefit Coverage Dependency and Government Policy Deferral

Application of coverage criteria is dependent upon an individual's benefit coverage at the time of the request. Specifications pertaining to Medicare and Medicaid can be found in the 'Applicable State and Federal Regulations' of this policy document. If there is a conflict between this policy and any relevant government policy for a particular member (e.g., Local Coverage Determinations (LCDs) or National Coverage Determinations (NCDs) for Medicare and/or state coverage for Medicaid), the government policy will be used to make the determination.

Benefit coverage is determined by the member's plan at time of request; requests inconsistent with individual benefit coverage may be denied.
Coverage determinations will defer to applicable government policies (LCDs/NCDs) where they conflict with this policy.

Documentation Required

Specimen Handling and Pre-Treatment Sampling

For valid and timely laboratory diagnosis when measuring total homocysteine (tHcy), follow specimen handling and pre-treatment sampling recommendations: centrifuge blood/plasma samples within one hour of collection and keep at 4°C (refrigerated) or freeze until analysis. Do not measure free homocysteine as a substitute for total homocysteine.

Ordering Requirements

Step Therapy

Ordering requirement — specimen handling and pretreatment collection

For suspected remethylation disorders and newborn screening follow‑up, ordering clinicians must ensure proper specimen handling (rapid centrifugation and cold storage) and collect pretreatment plasma/urine samples for recommended analytes when tHcy is elevated.

Measure plasma tHcy as the frontline test for suspected remethylation disorders.
Collect plasma/urine for MMA, methionine, folate, and B12 before treatment if tHcy is high.

Note

Ordering guidance — no additional restrictions specified

The policy does not impose explicit ordering restrictions; clinicians should follow standard clinical practice for suspected cases and newborn screening workflows and use the tests and sequences described in the policy (dried blood spot screening, second‑tier tHcy, plasma confirmation) as clinically indicated.

Not Covered / Exclusions

The document does not list explicit per-test exclusions in this section, but it discourages and does not recommend routine use of free homocysteine testing as a substitute for total homocysteine measurement.

The pyridoxine (B6) challenge test has been removed from the policy’s laboratory coverage criteria and is considered outside the scope of laboratory testing for this policy. Measurement of biochemical markers (for example, tHcy) remains the laboratory-based approach for diagnosis and monitoring.

Frequency Limits

Frequency limits

Frequency limits specified in this document sectionNot specified

ImplicationRefer to individualized monitoring guidance elsewhere in policy

Action for providersFollow treating clinician judgment and benefit-specific rules for repeat testing

Monitoring frequency

Tests with individualized frequencytHcy, amino acids, folate, vitamin B12

Reason for individualizationFrequency varies by severity, treatment plan, and patient age

Clinical action

Definitions

tHcy (total homocysteine) — definition and reference ranges

Definition of tHcyTotal homocysteine (tHcy): all forms of homocysteine measured together in plasma

Normal referenceControl <15 µmol/L

Pathologic examplesNeonate with homocystinuria: 50 to >100 µmol/L; untreated older individual: >100 µmol/L

CBS (cystathionine β-synthase)

TermCBS = cystathionine β-synthase

Clinical relevanceDeficiency of CBS causes classic homocystinuria (CBS deficiency)

Confirmatory testing

Background

Homocystinuria is an inherited metabolic disorder most commonly caused by deficiency of cystathionine-β-synthase (CBS). CBS deficiency leads to accumulation of homocysteine and methionine, producing clinical features affecting the eyes, skeleton, neurodevelopment, and thrombotic risk. Early detection through newborn screening and timely biochemical confirmation with plasma total homocysteine (tHcy) improves outcomes.

Policy Summary

PayerBlue Cross Blue Shield - Louisiana

PolicyTesting of Homocysteine Metabolism-Related Conditions

Policy CodePolicy AHS - M2141

Change TypeRemoved pyridoxine challengeremoved select genetic criteria and codesCPT cleanup

Effective DateMay 15, 2022

Next Review Date

SourceLink

On This Page

Monitoring during therapy: Monitor tHcy, amino acids, folate, and vitamin B12 during therapy; frequency individualized based on severity, treatment, and age.

Target tHcy <50 µmol/L in pyridoxine-responsive patients and approximately 120 µmol/L total (≈11 µmol/L free) in pyridoxine-unresponsive patients.

Measure plasma total homocysteine as the frontline diagnostic test in symptomatic individuals suspected of homocystinuria; plasma assays preferred when plasma processing is possible.

Plasma tHcy is recommended as the frontline test for diagnosis and confirmation; dried blood spot tHcy acceptable if plasma processing is not possible.

inv-24: Diagnostic testing and therapeutic monitoring of individuals over 18 with suspected or confirmed CBS deficiency using plasma total homocysteine.

Adult diagnostic testing (age >18): For individuals over 18 years of age with suspected homocystinuria due to CBS deficiency, plasma total homocysteine (tHcy) testing meets coverage criteria to establish the diagnosis.

tHcy measurement used to establish classic homocystinuria; Met measurement can corroborate diagnosis.

Therapeutic monitoring in confirmed CBS deficiency: For monitoring response to therapy in individuals with confirmed CBS deficiency, plasma total homocysteine testing meets coverage criteria.

Use tHcy to assess treatment response and pyridoxine (B6) responsiveness; target levels vary by responsiveness.

inv-25: Diagnosis of suspected homocystinuria or remethylation disorders (neurological, visual, hematological, thrombotic signs), newborn screening when abnormal methionine or Met/Phe ratio, and monitoring during therapy.

Diagnosis for clinical suspicion: Measure total homocysteine (tHcy) in any patient presenting with neurological, visual, hematological, or thrombotic signs, subacute spinal cord degeneration, atypical haemolytic uremic syndrome, or unexplained vascular thrombosis to evaluate for homocystinuria or remethylation disorders.

E-HOD strongly recommends plasma tHcy as the initial investigation in such patients; obtain MMA, methionine, folate and B12 if tHcy is high before treatment is started.

Newborn screening trigger: When newborn methionine or Met:Phe ratio is abnormal, perform second-tier tHcy on dried blood spots or follow-up plasma testing to detect homocystinuria or remethylation disorders.

Using tHcy as a second-tier marker increases screening specificity; feasibility for some disorders is uncertain.

Monitoring during therapy: During therapy for homocystinuria or remethylation disorders, monitor tHcy, amino acids, folate and vitamin B12 at frequencies individualized to the patient based on severity, treatment, and age.

Targets: <50 µmol/L total tHcy in pyridoxine-responsive patients; ~120 µmol/L total (≈11 µmol/L free) in pyridoxine-unresponsive patients.

Pyridoxine-responsive: total tHcy <50 µmol/L; Pyridoxine-unresponsive: ~120 µmol/L total (≈11 µmol/L free)

Centrifuge blood/plasma within one hour of collection.
Store plasma at 4°C or freeze until analysis.
Measure total homocysteine (tHcy); free homocysteine measurement is not recommended.

Documentation Required

Specimen Handling and Additional Testing

When tHcy is measured for suspected remethylation disorders or when elevated tHcy is identified, obtain plasma and urine samples for additional testing (e.g., methylmalonic acid [MMA], methionine, folate, vitamin B12) before initiating treatment. Consider quantitative plasma amino acids analysis and/or urine/plasma testing as clinically indicated. Dried blood spot tHcy measurement may be used if plasma processing is not possible.

If tHcy is high, collect plasma and urine for MMA, methionine, folate and vitamin B12 prior to starting treatment.
Use quantitative plasma amino acids analysis and/or plasma/urine tHcy as indicated.
Dried blood spot tHcy measurement is acceptable when plasma processing is not possible.

Note

Coverage Requirements Summary

Newborn screening and follow-up testing: Newborn screening for homocysteine-related conditions meets coverage criteria for screening (including dried blood spot testing for homocystinuria and hypermethioninemia). If initial newborn methionine exceeds the program cut-off, a repeat dried blood specimen or quantitative plasma amino acids and plasma tHcy analysis meets coverage criteria. For adults (>18 years) with suspected or confirmed CBS deficiency, plasma total homocysteine testing meets coverage criteria for diagnosis and monitoring therapy.

Newborn screening for classic homocystinuria (CBS deficiency) via quantitative plasma amino acids and/or plasma/urine tHcy is covered.
Repeat dried blood specimen or quantitative plasma amino acids plus plasma tHcy when newborn methionine exceeds cut-off is covered.
Plasma total homocysteine testing for individuals >18 years with suspected or confirmed CBS deficiency is covered.

Adjust monitoring schedule per clinician judgment and guideline recommendations

Confirmation can include measurement of cystathionine synthase activity or CBS gene mutation analysis

tHcy (term)

AbbreviationtHcy = total homocysteine

SpecimenMeasured in plasma (dried blood spot acceptable for newborn screening if plasma processing not possible)

Clinical useFrontline diagnostic test for suspected remethylation disorders and homocystinuria

CBS deficiency — definition and confirmation

ConditionCBS deficiency (Cystathionine beta-synthase deficiency)

Diagnostic confirmationConfirm by measuring cystathionine synthase activity in cultured fibroblasts or plasma and/or by CBS gene mutation analysis

Gold standardEnzyme assay in cultured fibroblasts is considered the gold standard for confirmation