Left Atrial Thrombus Despite Anticoagulation: The Importance Of Homocysteine.

Patients in atrial fibrillation may have left atrial thrombi or strokes despite adequate anticoagulation. It is important to consider elevated plasma total homocysteine (tHcy) as a treatable clotting factor that may explain such cases. Metabolic B12 deficiency is common even in patients with a "normal" serum B12. Measurement of holotranscobalamin, methylmalonic acid or, in folate-replete patients, tHcy are necessary to diagnose metabolic B12 deficiency when the serum B12 is below 400 pmol/L. Elevated tHcy quadruples the risk of stroke in atrial fibrillation, and is far more common than the usual clotting factors for which testing is commonly performed: among patients attending.