Heparin-induced thrombocytopenia incidence in the ICU: preliminary results

Introduction

Heparin-induced thrombocytopenia (HIT) is a life-threatening and limb-threatening immune-mediated prothrombotic complication caused by heparinic drugs. The aim of this study was to evaluate the incidence of HIT in a mixed ICU population.

Methods

Patients admitted to the ICU of a regional referral center (Careggi Teaching Hospital, Florence, Italy) who underwent unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH) administration were prospectively observed from October 2008. Exclusion criteria: haematological malignancy, platelet count <50,000/mm³ before anticoagulant treatment. After anticoagulant administration start, patients showing a fall of platelet count >50% or a nadir <150,000/mm³ were clinically evaluated with the 4 T score (4Ts) [1]: cases with a 4Ts of at least 2 were investigated with the laboratory antigen assay, the ELISA. Positive tests underwent to a functional confirmation test, the heparin-induced platelet activation (HIPA) test [2].

Results

Preliminary results refer to the period from the start to August 2009. Patients admitted to the ICU were 369; 327 enrolled for the study. Clinical evaluation with 4Ts was performed for 31 patients, 23 of 31 (74%) had a value of at least 2; eight of 23 were on UFH and the remaining 15 on LMWH. Potential etiologies of thrombocytopenia have been considered: 21 patients were septic, three were on extracorporeal membrane oxygenation, two were admitted to the ICU due to cardiogenic shock. The ELISA test resulted positive in three of 23 (13%) suspected HIT cases; none of the three cases resulted positive in the HIPA test, so HIT was excluded. The medium 4Ts of the 23 suspected HIT cases was 4.1 ± 1.7 whereas 4Ts did not differ between patients with positive and negative ELISA test.

Conclusions

HIT incidence in the ICU is extremely rare, with no cases shown in this study. HIT was suspected in 23 of 327 patients (7.03%), but the HIT incidence was 0.0%. ICU patients show numerous potential etiologies of thrombocytopenia and in this population sepsis was the most common.