How and when to monitor a patient treated with low molecular weight heparin

Low molecular weight heparins (LMWHs) are as efficient as unfractionated he parin (UFH) for prevention and treatment of thromboembolism. There is no ev idence that monitoring the dose improves the clinical efficacy. In contrast , any overdosage increases the risk of hemorrhage. Because renal function p lays a significant role in the elimination of LMWH, curative treatment shou ld be monitored with an anti-factor Xa assay in patients presenting renal i nsufficiency, in the elderly, and in patients presenting an increased hemor rhagic risk. It is advisable to sample the patient at peak activity (3 to 5 hours after the subcutaneous [sc] administration) and to target the mean a nti-factor Xa activity that was found efficient and safe in the clinical tr ial. This target is different for each LMWH and each dose regimen.