Homocyst(e)ine, Plasma

CPT: 83090
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Test Details

Use

Screen patients who may be at risk for heart disease and stroke

Limitations

This test is not intended for use in the diagnosis of folate or vitamin B12 deficiency. Anemia Profile, Megaloblastic [706960] should be used for this application.

Methodology

Enzymatic

Reference Interval

0.0−15.0 μmol/L

Additional Information

Severe homocysteinemia is typically caused by a rare inborn error of metabolism.1,2 The most common defect that can produce levels >100 μmol/L is homozygous cystathionine-β-synthase (CS) deficiency, which occurs with an incidence of 1 per 300,000 live births. About 1% of the population has heterozygous CS deficiency, a condition that typically results in moderate to intermediate hyperhomocysteinemia. Individuals with CS deficiency are at increased risk for occlusive vascular disease.1,2 Individuals with a thermolabile variant of the enzyme methylene-tetrahydrofolate reductase can have high normal to moderately elevated levels of homocysteine.1,2 Homocysteine can be considered to be an independent risk factor for the development of cardiovascular disease.1-3 Patients with cardiovascular disease, including heart disease, stroke, peripheral vascular disease, and thromboembolic disease generally have higher homocysteine levels than matched controls. The results of a large number of epidemiological studies have been analyzed through a meta-analysis.1 The increased risk, or odds ratio (OR), for coronary artery disease in patients with increased homocysteine levels was estimated to be 1.7. The OR for stroke was estimated to be 2.5 and the OR for peripheral vascular disease was estimated to be 6.8. Several conditions, other than specific genetic defects or cardiovascular disease, have been associated with hyperhomocysteinemia.1 These include vitamin deficiency, advanced age, hypothyroidism, impaired kidney function, and systemic lupus erythematosus. Medications including nicotinic acid, theophylline, methotrexate, and L-dopa have been reported to cause elevated homocysteine levels.

Specimen Requirements

Specimen

Plasma (preferred); serum is acceptable.

Volume

2 mL

Minimum Volume

1 mL

Container

Lavender-top (EDTA) tube, green-top (heparin) tube, red-top tube, or gel-barrier tube

Patient Preparation

A fasting specimen is preferred to establish baseline values or monitor treatment.

Collection

Separate plasma or serum from cells immediately to avoid a false elevation of homocysteine. After one hour at room temperature, a 10% increase may be seen. Transfer plasma or serum to a plastic transport tube (see Causes for Rejection). Homocysteine results increase by approximately 35% and 75% for samples not centrifuged and/or not separated from the clot for periods of four and 24 hours, respectively. Serum values are expected to be higher than plasma values. Slightly higher values are observed in nonfasting patients.

Storage Instructions

Room temperature. Stable at room temperature or refrigerated for 14 days. Stable frozen for six months.

Causes for Rejection

Specimen received not separated from cells (do not respin a gel-barrier tube to harvest additional serum); gross hemolysis (eg, bright red or cherry red); whole blood tube without a gel separator; plasma from a light blue-top (sodium citrate) tube or yellow-top (ACD) tube used for coagulation studies (liquid citrate tubes have a dilutional effect of approximately 1.2 on this assay and are not approved for use); gross lipemia

Clinical Information

Footnotes

1. Malinow MR, Bostom AG, Krauss RM. Homocyst(e)ine, diet, and cardiovascular diseases: A statement for healthcare professionals from the nutrition committee, American Heart Association. Circulation. 1999; 99(1):178-182. 9884399
2. Clarke R, Stansbie D. Assessment of homocysteine as a cardiovascular risk factor in clinical practice. Ann Clin Biochem. 2001; 38(Pt 6):624-632. 11732645
3. Herrmann W. The importance of hyperhomocysteinemia as a risk factor for diseases: An overview. Clin Chem Lab Med. 2001; 39(8):666-674.11592431

References

Fortin LJ, Genest J Jr. Measurement of homocyst(e)ine in the prediction of arteriosclerosis. Clin Biochem. 1995; 28(2):155-162 (review). 7628074
Kang SS, Wong PW, Malinow MR. Hyperhomocyst(e)inemia as a risk factor for occlusive vascular disease. Annu Rev Nutr. 1992; 12:279-298. 1503807
Malinow MR. Plasma homocyst(e)ine and arterial occlusive diseases: A mini review. Clin Chem. 1995; 41(1):173-176 (review). 7813076
Robinson K, Mayer E, Jacobsen DW. Homocysteine and coronary artery disease. Cleve Clin J Med. 1994; 61(6):438-450 (review). 7828335
Ueland PM, Refsum H, Stabler SP, et al. Total homocysteine in plasma or serum: Methods and clinical applications. Clin Chem. 1993; 39(9):1764-1779 (review). 8375046
Verhoef P, Stampfer MJ, Buring JE, et al. Homocysteine metabolism and risk of myocardial infarction: Relation with vitamins B6, B12, and folate. Am J Epidemiol. 1996; 143(9):845-859. 8610698

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
706994 Homocyst(e)ine, Plasma 13965-9 707009 Homocyst(e)ine, Plasma umol/L 13965-9

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