• Mark Andrew Crowther, Deborah J Cook, Martin Albert, David Williamson, Maureen Meade, John Granton, Yoanna Skrobik, Stephan Langevin, Sangeeta Mehta, Paul Hebert, Gordon H Guyatt, William Geerts, Christian Rabbat, James Douketis, Nicole Zytaruk, Joanne Sheppard, Andreas Greinacher, Theodore E Warkentin, and Canadian Critical Care Trials Group.
• Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada. crowthrm@mcmaster.ca
• J Crit Care. 2010 Jun 1; 25 (2): 287-93.

BackgroundHeparin-induced thrombocytopenia (HIT) is commonly considered but rarely confirmed in critically ill patients. The 4Ts score (Thrombocytopenia, Timing of thrombocytopenia, Thrombosis, and oTher reason) might identify individual patients at risk of having this disorder.ObjectiveThe aim of the study was to evaluate the value of the 4Ts HIT score in comparison with the serotonin-release assay (SRA) in critically ill patients.MethodsThis study describes the combined results of 3 prospective studies enrolling critically ill patients who were investigated for HIT if platelets fell to less than 50 x 10(9)/L or if platelet counts decreased to less than 50% of the value upon intensive care unit admission. We confirmed HIT by a positive platelet SRA. We assigned a 4Ts score blinded to SRA results to all 50 patients investigated for HIT; those with positive SRA results were scored in duplicate.ResultsOf 528 patients, 50 (9.5%) were investigated for HIT; 39 (78%) of 50 (64%-88%) of these patients were scored as "low probability" by 4Ts score and none had a positive SRA. Of 49 patients who underwent SRA testing because of thrombocytopenia, only 2 (4.1%; 0.5-14.0) had a positive SRA (1 with a moderate 4Ts score and 1 with a high 4Ts score). Therefore, the overall incidence of HIT confirmed by SRA was 2 (0.4%) of 528 (0.04%-1.4%).ConclusionsSignificant thrombocytopenia during heparin administration occurred in 9.5% of critically ill patients, but HIT was confirmed in only 4.1% of those undergoing testing, for an overall incidence of 0.4%. A low 4Ts score occurred in 78% of patients investigated for HIT; none of these patients had a positive SRA. We conclude that HIT is uncommon in critically ill patients and that the 4Ts score is worthy of further evaluation in this patient population.Copyright (c) 2010. Published by Elsevier Inc.

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