homocysteine (Hcy)
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p516-517
2025-06-03
503
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). 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.
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.
Contraindications
• Patients whose creatinine levels exceed 1.5 mg/dL are not candidates for methionine loading. Elevated creatinine levels indicate malfunctioning kidneys that cannot effectively filter methionine.
Interfering factors
• Patients with renal impairment have elevated levels of homo cysteine because of poor excretion of the protein.
• Men usually have higher levels of homocysteine than women. Most likely, this is because of higher creatinine values and greater muscle mass. Values also increase with age.
• Smoking is associated with increased homocysteine levels.
* Drugs that may cause increased levels include azaribine, carbamazepine, methotrexate, nitrous oxide, and phenytoin.
* Oral contraceptives containing estrogen may alter the metabolism of homocysteine.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: yes (10-12 hours)
• Blood tube commonly used: purple, green, or blue
• For methionine loading, the patient ingests approximately 100 mg/kg of methionine after fasting for 10 to 12 hours. A blood sample is obtained. Repeat blood samples are collected at 2, 4, 8, 12, and 24 hours to compare levels of B vitamins and amino acids in the plasma.
• In the laboratory, the blood should be spun down within 30 minutes in order to avoid false elevation caused by release of homocysteine from RBCs.
Abnormal findings
Increased levels
- Cardiovascular disease
- Cerebrovascular disease
- Peripheral vascular disease
- Cystinuria
- Vitamin B6 or B12 deficiency
- Folate deficiency
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