WHAT IS HOMOCYSTEINE TEST?
Homocysteine is an amino acid that results from the metabolism of methionine by the B vitamins cobalamin, folate, pyridoxine, and riboflavin. The breakdown of methionine to homocysteine is counterbalanced by choline and betaine, coenzymes that convert homocysteine back into methionine. Although the exact function of homocysteine is not known, it is postulated that it may cause damage to the vascular endothelium or have a part in the causation of thrombi. Homocystinuria is an inherited disease in which persons who lack the enzymes that help control homocysteine levels demonstrate severe cardiovascular disease at a young age. Hyperhomocysteinemia has been established in recent years as an independent risk factor for cardiovascular disease, including atherosclerosis, carotid artery stenosis, coronary artery disease, stroke, peripheral vascular disease, and venous thrombosis. Elevated levels are also associated with fetal neural tube defects, recurrent spontaneous abortion, placental infarction, and reduced cognitive functioning in the elderly, and are considered to be a uremic toxin. Because firmly established reference ranges do not yet exist, homocysteine may often not be measured. Instead, physicians measure vitamin levels and, when vitamin deficiencies are found, infer elevated homocysteine levels. In other situations, homocysteine levels may be used as a functional test to determine folate deficiency because there exists an inverse relationship between the two values. The plasma test is best for this purpose and for assessment of cardiovascular risk. The urine homocysteine test should NOT be used in clients with renal failure, although it has been.