Assessment of a modified 4T scoring system for heparin-induced thrombocytopenia in critically ill patients

The purpose of the study is to determine if a modified 4T (m4T) scoring system, which omits clinical evaluation of other thrombocytopenic etiologies, is different from the 4T scoring system's probability to predict a positive heparin-induced thrombocytopenia (HIT) laboratory test in the intensive care unit.

This is a single-centered retrospective analysis of critically ill adults who had an enzyme-linked immunosorbent assay antiplatelet factor 4 antibody (ELISA anti-PF4 Ab) ordered. Patients were identified as HIT positive (optical density, ≥0.40) or HIT negative (optical density, <0.40) based on the ELISA anti-PF4 Ab. Both 4T and m4T scores were calculated, and the diagnostic accuracy was compared using paired receiver operating characteristic curves.

A total of 1487 adult intensive care unit patients with an ELISA anti-PF4 Ab ordered between January 2007 and December 2009 were eligible for study enrollment. Application of exclusion criteria and random selection yielded a total of 232 patients included for analysis (58 HIT-positive and 174 HIT-negative patients). The area under the curve for the 4T and m4T scores were 0.683 (95% confidence interval, 0.604-0.762) and 0.680 (95% confidence interval, 0.600-0.759), respectively (P=.065).

This study does not show a difference in the probability of the m4T and 4T scoring systems to predict a positive ELISA anti-PF4 Ab test in the critically ill patient population. Further prospective studies are needed to validate the m4T scoring system.