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Homocysteine, Total

Homocystine

Test Codes

EPIC: LAB93, Beaker: HCY, Antrim: 30380

Department

Chemistry

Instructions

A fasting specimen is preferred, but not required.

Specimen Collection Criteria

Collect: One Gold-top SST tube. (Minimum Whole Blood: 4.0 mL)

SST tubes should be centrifuged within 1 hour of collection.

Physician Office/Draw Specimen Preparation

Let SST specimens clot then immediately centrifuge to separate serum from cells within one hour of collection. Refrigerate (2-8°C or 36-46°F) the centrifuged SST tube within two hours of collection.

Preparation for Courier Transport

Transport: Centrifuged SST tube refrigerated (2-8°C or 36-46°F). (Minimum: 0.5 mL)

Rejection Criteria

• Hemolyzed specimens.
• Specimens not collected and processed as indicated.

In-Lab Processing

Let SST specimens clot then immediately centrifuge to separate serum from cells within one hour of collection. If the specimen will not be tested within 48 hours of collection, transfer serum to a plastic aliquot tube and freeze (-20°C/-4°F or below). Do NOT freeze the centrifuged collection tube.

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers^® with Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 48 hours
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes, Green-top Tubes, and Microtainers^® without Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 48 hours
Frozen (-20°C/-4°F or below): 13 weeks

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Dearborn Chemistry Laboratory
Royal Oak Automated Chemistry Laboratory

Performed

Sunday – Saturday, 24 hours a day.
Results available within 24 hours of receipt in the Laboratory.

Reference Range

4-10 micromoles/L:  Desirable Level.

Test Methodology

Chemiluminescence.

Interpretation

Total homocysteine is considered to be a risk factor for cardiovascular disease. The risk increases progressively with homocysteine concentration. Maintenance of homocysteine levels below 10 micromoles/L is suggested by some investigators and levels greater than 15 micromoles/L are considered abnormal in patients under evaluation for cardiovascular and neurovascular disease.

In addition to recognized disease states, increased homocysteine levels have been reported in patients receiving a variety of drugs - includes S-adenosyl-methionine, methotrexate, nicotinic acid, theophylline, nitrous oxide, and L-dopa.

Homocysteine results may be falsely elevated when the sample is not handled correctly. Serum must be separated promptly from cells within one hour of blood collection.

Blood samples obtained after an individual has consumed a heavy meal (particularly if rich in protein) have been associated with a 15-20% increase in homocysteine. Therefore, heavy meals should be avoided 6-12 hours before blood sampling. A light meal has not been shown to affect the homocysteine level.

Clinical Utility

Elevated homocysteine levels are found in patients with recessively inherited metabolic defects such as cystathionine ß-synthase deficiency and decreased methyl tetrahydrofolate reductase activity. Individuals with cystathionine ß-synthase deficiency may have serum homocysteine levels up to 200 micromoles/L.

Homocysteine levels may be elevated in vitamin B₆, B₁₂, and folate deficiencies.

Homocysteine has been shown to be an independent risk factor for atherosclerotic vascular disease. Homocysteine levels greater than the 90th percentile of normal are associated with increased risk for acute myocardial infarction. The risk for coronary vascular disease increases progressively with homocysteine concentration. There is a 13-fold increase in risk associated with a level of 19 micromoles/L as compared to a 9 micromoles/L homocysteine concentration.

Reference

Welch, GN, Loscalzo J. Homocysteine and atherothrombosis. New Eng. J. Med 338:1042-1050;1998.

CPT Codes

83090

Contacts

Last Updated

10/31/2024