• Timothy A Morris, Selene Castrejon, Gehan Devendra, and Anthony C Gamst.
• Division of Pulmonary and Critical Care Medicine, Department of Family and Preventative Medicine, University of San Diego, CA, USA. t1morris@ucsd.edu
• Chest. 2007 Oct 1; 132 (4): 113111391131-9.

BackgroundLow-molecular-weight heparin (LMWH) is a popular alternative to unfractionated heparin (UH) for the treatment of pulmonary embolism (PE) and deep vein thrombosis (DVT), in part based on the perception of a lower risk for heparin-induced thrombocytopenia (HIT). To investigate the evidence supporting this perception, we performed a metaanalysis to compare the incidence of thrombocytopenia between LMWH and UH during PE and/or DVT treatment.MethodsRandomized trials comparing LMWH with UH for PE and/or DVT treatment were searched for in the MEDLINE database, bibliographies, and by correspondence with published investigators. Two reviewers independently selected high-quality studies and extracted data regarding heparin-associated thrombocytopenia (HAT), HIT confirmed by laboratory testing, and heparin-induced thrombocytopenia with thrombosis (HITT). Outcome rates between LMWH and UH were compared using a binomial, generalized linear mixed model with a logit link and Gaussian random effects for study.ResultsThirteen studies involving 5,275 patients met inclusion criteria. There were no statistically significant differences in HAT rates between the two treatments (LMWH, 1.2%; UH, 1.5%; p = 0.246). The incidence of documented HIT and HITT was too low to make an adequate comparison between groups.ConclusionsOur review disclosed no statistically significant difference in HAT between LMWH and UH and insufficient evidence to conclude that HIT and HITT rates were different between them. There was no evidence from randomized comparative trials to support the contention that patients receiving treatment for PE or DVT with UH are more prone to these complications than those receiving LMWH.

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