Mosby's Diagnostic and Laboratory Test Reference

Author:Pagana, Kathleen Deska & Pagana, Timothy J. [Pagana, Kathleen Deska]
Language: eng
Format: mobi
ISBN: 9780323170765
Publisher: Elsevier Health Sciences
Published: 2012-10-05T00:00:00+00:00

Abnormal findings

Cardiac arrhythmia

Ischemic changes

notes

homocysteine (Hcy)

Type of test

Blood

Normal findings

4-14 µmol/L

(Levels may increase with age.)

Test explanation and related physiology

Homocysteine is an intermediate amino acid formed during the metabolism of methionine. Increasing evidence suggests that elevated blood levels of homocysteine may act as an independent risk factor for ischemic heart disease, cerebrovascular disease, peripheral arterial disease, and venous thrombosis. Homocysteine appears to promote the progression of atherosclerosis by causing endothelial damage, promoting low-density lipoprotein (LDL) deposition, and promoting vascular smooth muscle growth.

Dietary deficiency of vitamins B6, B12, or folate is the most common cause of elevated homocysteine. These vitamins are essential for the enzymatic metabolism of homocysteine to methionine (a protein). Because of the relationship of homocysteine to these vitamins, homocysteine blood levels are helpful in the diagnosis of deficiency syndromes associated with these vitamins. Homocysteine levels are elevated in patients with megaloblastic anemia. Some practitioners recommend homocysteine testing in patients with known poor nutritional status (alcoholics, drug abusers) and the elderly. Homocysteine is elevated in children with inborn errors of methionine metabolism. Some researchers believe that elevated levels of homocysteine can be treated by administration of vitamins B6, B12, and folate.

Both fasting and postmethionine loading levels of homocysteine can be measured. In general, homocysteine levels less than 12 are considered optimal, levels from 12 to 15 are borderline, and levels greater than 15 are associated with high risk of vascular disease. When blood levels are elevated, urine homocysteine levels are also increased.

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