Lab Dept:

Chemistry

Test Name:

HOMOCYSTEINE, TOTAL, PLASMA

General Information

Lab Order Codes:

HOMC

Synonyms:

Amino Acid Homocysteine

CPT Codes:

83090 - Homocysteine

Test Includes:

Homocysteine, Total, Plasma measured in mcmol/L.

Logistics

Test Indications:

Homocysteine (HCY) represents the main biochemical marker of several primary and secondary disorders of methionine metabolism.

Primary enzyme defects include: Cystathionine synthase (CS) deficiency; Methylenetetrahydrofolate reductase (MTHFR) deficiency and thermolabile variant; Methionine syntase (MS) deficiency

Secondary to genetic defects of cofactors metabolism include: Vitamin B(6); Vitamin B(12); Folic acid

Lab Testing Sections:

Chemistry - Sendouts

Referred to:

Mayo Medical Laboratories (Test# 80379)

Phone Numbers:

Minneapolis:

Saint Paul:

612-813-6280

651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

1 – 3 days, test set-up Monday – Saturday

Special Instructions:

See Patient Preparation

Specimen

Specimen Type:

Blood

Container:

Lavender top (EDTA) tube

Draw Volume:

1.2 mL (Minimum: 0.5 mL) blood

Processed Volume:

0.4 mL (Minimum: 0.15 mL) plasma

Collection:

Routine venipuncture from fasting patient. Mix sample by gentle inversion. Place specimen on wet ice and deliver to the lab for immediate processing.

Special Processing:

Lab Staff: Centrifuge specimen within 1 hour of draw. Remove plasma aliquot into a screw-capped round bottom plastic vial. Store and ship at refrigerated temperatures. Forward promptly.

Patient Preparation:

Patient should be fasting (if possible) prior to specimen collection. A 4 hour fast is preferred.

Sample Rejection:

Hemolysis; warm specimens; mislabeled or unlabeled specimens

Interpretive

Reference Range:

Homocysteine levels of >13 mcmol/L are considered abnormal, in patients under evaluation for Cardiovascular disease and Neurovascular disease.

Hyperhomcysteinemia suggests that genetic and nutritional factors are potentially involved in the etiology of the disease.

Response to dietary treatment can be evaluated by monitoring plasma homocysteine levels over time.

Critical Values:

N/A

Limitations:

Higher plasma homocysteine concentrations are detected in non-fasting specimens.

Factors influencing plasma homocysteine concentration levels include:

Gender: Approximately 25% higher in men vs. age-matched premenopausal women.

Age: Increases with age

Lifestyle: Smoking, lack of exercise

Diet: Cofactor deficiencies

Renal function

Disease states: Psoriasis, Leukemia

Medications Influencing Plasma HCY levels:

Methotrexate: 5-methyltetrahydrofolate depletion

Azuridine: Vitamin B6 antagonist

Nitrous Oxide: Inactivation vitamin B12

Phenytoin: Interference with folate metabolism

Carbamezapine: Interference with folate metabolism

Oral contraceptives: Estrogen-induced vitamin B6 deficiency

Penicillamine: Reduction in homocysteine levels

Methodology:

100 uL of plasma are spiked with d₈-homocystine (2 nmoles) added as internal standard. After specimen reduction and deproteinization, the analysis by tandem mass spectrometry is performed in the multiple reaction monitoring mode.

References:

Mayo Medical Laboratories Web Page July 2010

Updates:

11/16/2010: Units change from umol/L to mcmol/L.