Screen patients who may be at risk for heart disease and stroke
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.
Plasma (preferred); serum is acceptable.
Lavender-top (EDTA) tube, green-top (heparin) tube, red-top tube, or gel-barrier tube
A fasting specimen is preferred to establish baseline values or monitor treatment.
Plasma: It is important to centrifuge blood samples for plasma collection immediately after collection to separate the plasma from the blood cells. If immediate centrifugation is not possible, collected blood specimens should be kept on ice and centrifuged within an hour.
Serum:Allow 45 minutes for serum to clot and centrifuge to separate serum from cells immediately thereafter
Stable at room temperature or refrigerated for 14 days. Stable frozen for six months.
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