Test Directory

Homocysteine, Total, Serum

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Updated Test Information:

Test Description
Homocysteine, Total, Serum

Cystathionine beta-synthase deficiency; Methylenetetrahydrofolate reductase deficiency (MTHFR); MTHFR deficiency; Methionine synthase deficiency; Cobalamin (Cbl) metabolism; Methyl-Cobalamin deficiency; Adenosyl-cobalamin deficiency; Cbl C2 deficiency; Cbl D2 deficiency; Cbl F3 deficiency; Cbl D-Var1 deficiency; Cbl E deficiency; Cbl G deficiency; Transcobalamin II deficiency; Adenosylhomocysteinase (AHCY) deficiency; Glycine N-methyltransferase (GNMT) deficiency; Methionine adenosyltransferase (MAT) I/III deficiency; Cobalamin C2 deficiency; Cobalamin D2 deficiency; Cobalamin F3 deficiency; Cobalamin D-Variant 1 deficiency; Cobalamin E deficiency; Cobalamin G deficiency

Test ID
General Information

Useful for screening patients suspected of having an inherited disorder of methionine metabolism including:

  • Cystathionine beta-synthase deficiency (homocystinuria)

  • Methylenetetrahydrofolate reductase deficiency (MTHFR) and its thermolabile variants:

    • Methionine synthase deficiency

    • Cobalamin (Cbl) metabolism

    • Combined methyl-Cbl and adenosyl-Cbl deficiencies: Cbl C2, Cbl D2, and Cbl F3 deficiencies

    • Methyl-Cbl specific deficiencies: Cbl D-Var1, Cbl E, and Cbl G deficiencies

    • Transcobalamin II deficiency

    • Adenosylhomocysteinase (AHCY) deficiency

    • Glycine N-methyltransferase (GNMT) deficiency

    • Methionine adenosyltransferase (MAT) I/III deficiency 

  • Screening and monitoring patients suspected of or confirmed with an inherited disorder of methionine metabolism

  • Evaluating individuals with suspected deficiency of B12 or folate

Specimen Type


Specimen Requirements

  • Preferred: Red Top

  • Acceptable: Serum Gel (SST)

Additional Processing Details

Centrifuge and aliquot serum into plastic vial within 4 hours of collection.

Required Information

  • Refrigerated (preferred): 28 days

  • Ambient: 28 days

  • Frozen: 309 days


  • Other factors that may influence and increase serum homocysteine include:

    • Age

    • Smoking

    • Poor diet/cofactor deficiencies

    • Chronic kidney disease/renal disease

    • Hypothyroidism

  • Medications that may increase homocysteine concentrations include:

    • Methotrexate: 5-Methyltetrahydrofolate depletion

    • Azuridine: Vitamin B6 antagonist

    • Nitrous oxide: Inactivation of methionine synthase

    • Phenytoin: Interference with folate metabolism

    • Carbamazepine: Interference with folate metabolism

    • Oral contraceptives: Estrogen-induced vitamin B6 deficiency


Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Estimated TAT

3-5 days

Testing Schedule



7 days

CPT Code(s)


Additional Information
Minimum Sample Volume

.10 mL

Reference Range File View/Download File
Performing Lab

Mayo Clinic

LOINC Code(s)