Measurement and use of total plasma homocysteine. American Society of Human Genetics/American College of Medical Genetics Test and Transfer Committee Working Group.

Hyperhomocysteinemia, which is a recognized independent risk factor for premature vascular occlusion, is defined as a fasting total plasma homocysteine (tHcy) level >15 microM. There may also be graded increased risks for persons with tHcy concentrations of 10-15 microM. The measurement of tHcy requires precise sample collection, immediate separation and freezing of plasma, and referral to a specialized laboratory. The etiologies of hyperhomocysteinemia are complex and involve both genetic and environmental factors. Because the inappropriate supplementation of involved cofactors can be harmful, it is important to identify the cause of hyperhomocysteinemia prior to treatment.