LMWH = UFH for thrombocytopenia

Clinical Question

What is the risk for thrombocytopenia with unfractionated heparin versus low-molecular-weight heparin in patients treated for acute venous thromboembolism?

Bottom Line

There was no difference in risk of thromboembolism between unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) in patients with acute deep venous thrombosis (DVT) or pulmonary embolism (PE). (LOE = 1a)


Morris TA, Castrejon S, Devendra G, Gamst AC. No difference in risk for thrombocytopenia during treatment of pulmonary embolism and deep venous thrombosis with either low-molecular-weight heparin or unfractionated heparin: a metaanalysis. Chest 2007:132(4):1131-1139.  [PMID:17646239]

Study Design

Meta-analysis (randomized controlled trials)




Inpatient (any location)


A thorough search of English language literature was done to identify randomized controlled trials comparing the incidence of thrombocytopenia with UFH versus LMWH in patients with objectively diagnosed DVT or PE. Two independent reviewers evaluated studies for inclusion and quality. Studies were rated on the basis of 9 criteria; a score of 8 was needed to be considered high enough quality for inclusion. Thrombocytopenia was defined as platelet counts between 80,000 mm3 to 120,000 mm3 or a decrease in platelets by at least 50%. A secondary analysis included all definitions of thrombocytopenia specified in the respective articles. The diagnosis of heparin-induced thrombocytopenia (HIT) required an objective test, such as a heparin-induced serotonin release assay, heparin-induced platelet aggregation, or heparin-platelet factor 4 (PF4) enzyme-linked immunosorbent assay. Heparin-induced thrombocytopenia thrombosis (HITT) was defined as thrombocytopenia with new arterial or venous thrombosis. Thirteen studies including 5275 patients were included for analysis of the primary outcome, 4 for the outcome of HIT, and 5 for HITT. The incidence of thrombocytopenia was 1.2% for enoxaparin-treated patients and 1.5% for those receiving UFH. Only a total of 5 patients had serologically confirmed HIT (2 receiving LMWH, 3 receiving UFH), and only 1 patient in the UFH group had HITT. These results may be limited by the lack of routine serologic testing for HIT among patients with thrombocytopenia.