Homocysteine

5 mL blood in EDTA or lithium heparin tube, collected after a 12 h fast, or after an oral methionine load (100 mg/kg body weight).

HPLC, immunoassay.

5-15 µmol/L.

If there is established vascular disease it is desirable that the fasting concentration is <10 µmol/L.

Diagnosis of homocystinuria and monitoring treatment.

Detection of mild hyperhomocysteinaemia as a risk factor for early onset cerebral and coronary atherosclerosis.

Mild hyperhomocysteinaemia is an established risk factor for atherosclerosis and vascular disease. However, lowering with vitamin B6 and folate did not improve outcome.

In classic homocystinuria, half the vascular complications are of venous origin. It has been established that high plasma homocysteine levels per se are a risk factor for deep vein thrombosis in the general population. The association was stronger among women than among men, increased with age, and remained significant after excluding other established factors for thrombosis.

In another case control study hyperhomocysteinaemia was found to be a risk factor for thrombosis in people younger than 40 years of age. The difference in the blood levels of homocysteine between controls and patients was particularly evident after a methionine load.

Elevated homocysteine levels may result from low levels of folic acid, vitamin B₆, or vitamin B₁₂, some drugs and renal impairment, as well as a number of inherited defects.

It remains unclear whether hyperhomocysteinaemia of different causes entails the same risk of thrombosis. It is also unknown whether vitamin supplementation, which can lower blood levels of homocysteine, will affect the natural history of venous thromboembolism.

The role of Thermolabile Methylene Tetrahydrofolate Reductase (MTHFR) caused by the 677C-->T mutation in thrombophilia is controversial.