Homocysteine
Test Mnemonic
HOMCYS
CPT Codes
- 83090 - QTY (1)
LOINC ®
13965-9
Performing Laboratory
Cleveland Clinic Laboratories
Specimen Requirements
| Volume | Type | Container | Collect Temperature | Transport Temperature | Special Instructions |
|---|---|---|---|---|---|
| 1 mL | Plasma | Lithium heparin PST (Lt. Green) | Place specimen on ice after draw. | Refrigerated | Centrifuge and separate plasma/serum from cells less than one hour after collection. If collected in a non-gel separator tube, centrifuge and transfer plasma/serum to a CCL tube and refrigerate. |
Alternate Specimen Requirements
| Volume | Type | Container | Collect Temperature | Transport Temperature | Special Instructions |
|---|---|---|---|---|---|
| 1 mL | Serum | SST (Gold) | Place specimen on ice after draw. | Refrigerated | Centrifuge and separate plasma/serum from cells less than one hour after collection. If collected in a non-gel separator tube, centrifuge and transfer plasma/serum to a CCL tube and refrigerate. |
Minimum Specimen Requirements
| Volume | Type | Container | Collect Temperature | Transport Temperature | Special Instructions |
|---|---|---|---|---|---|
| 0.5 mL |
Stability
| Environmental Condition | Description |
|---|---|
| Ambient | After separation from cells: 4 days |
| Refrigerated | After separation from cells: 4 weeks |
| Frozen | After separation from cells: 10 months |
Days Performed
Sun - Sat
Turnaround Time
8 hours
Methodology
| Name | Description |
|---|---|
| Enzymatic |
Special Info
Homocysteine is not available for Add-On test orders.
Clinical Info
The assay can assist in the diagnosis of patients suspected of having hyperhomocysteinemia or homocystinuria. Elevated tHcy levels are caused by four major factors, including: 1. genetic deficiencies in enzymes involved in Hcy metabolism such as cystathionine beta-synthase (CBS), methionine synthase (MS), and methylenetetrahydrofolate reductase (MTHFR); 2. nutritional deficiency in B vitamins such as B6, B12 and folate; 3. renal failure for effective amino acid clearance; and 4. drug interactions, such as with nitric oxide, methotrexate and phenytoin that interfere with Hcy metabolism. Excess Hcy is related to a higher risk of coronary heart disease, stroke, and peripheral vascular disease (fatty deposits in peripheral arteries). Specimens from patients who are on drug therapy involving S-adenosylmethionine may show falsely elevated levels of homocysteine. Patients who are taking methotrexate, carbamazepine, phenytoin, nitrous oxide, anticonvulsants, or 6-azauridine triacetate may have elevated levels of homocysteine due to their effect on the pathway.