Heparin-Induced Thrombocytopenia: Analysis of Risk Factors In Medicine Inpatients.

Heparin-induced thrombocytopenia (HIT) is an unpredictable drug reaction to heparin characterized by thrombocytopenia and increased risk of life threatening venous and/or arterial thrombosis. Although HIT is uncommon, it is a serious side effect in patients receiving heparin. Data are lacking if there are additional risk factors that may be associated with the development of HIT. Accordingly, the aim of this study was to identify the risk factors that may be associated with the development of HIT in medical inpatients receiving heparin.

This is a retrospective cohort study with 25,653 patients who were admitted to the medicine service and received heparin products (unfractionated heparin [UFH] or enoxaparin) in an urban teaching hospital in New York City from August 2005 to January 2010. Computerized discharge summaries, medical charts, radiology and laboratory reports were used in this retrospective study. Demographics such as age, gender and race were recorded. Details of medical history and hospital course of each patient was reviewed to obtain the known risk factors for HIT as well as possible confounding factors that may be related to the development of HIT. The diagnosis of HIT was confirmed if the platelet count dropped >50% from baseline and there was a positive laboratory HIT assay.

Fifty-five cases of in-hospital HIT (raw incidence, 0.21%, 95% CI [0.16, 0.28]) were observed (Table 1). After multivariate analysis, patients whose race was either Asian or Hispanic demonstrated an increased risk of developing HIT (relative risk [RR]= 2.61; 95% CI [1.10, 6.17]; p= 0.03 and RR= 2.21; 95% CI [1.22, 4.02]; p= 0.01 respectively). Additionally, patients who received full anticoagulation dose with UFH (RR= 3.66; 95% CI [1.98, 6.75]; p= <0.0001) or were exposed to heparin products for more than 5 days also had an increased risk of HIT (RR= 5.51; 95% CI [2.48, 12.2]; p= <0.0001 if heparin given 5 to 10 days, RR= 7.66; 95% CI [3.31, 17.8]; p= <0.0001 if heparin given more than 10 days). Moreover, patients who were on hemodialysis, carried a diagnosis of autoimmune disease, gout or heart failure remained as a independent risk factor for HIT (RR= 9.68; 95% CI [4.90, 19.1]; p= <0.0001, RR= 3.47; 95% CI [1.93, 6.26]; p= <0.0001, RR= 2.89; 95% CI [1.09, 7.68]; p= 0.03, and RR= 2.10; 95% CI [1.09, 4.08]; p= 0.03 respectively) (Table 2).

Among patients admitted to inpatient medicine service receiving heparin products, patients who were Asian or Hispanic, who were treated with full anticoagulation dose with UFH or who received heparin product >5 days were at increased risk of HIT. Furthermore, patients who were on hemodialysis, had autoimmune disease, gout and heart failure were also at increased risk of in-hospital HIT. The results suggest that when using heparin products in these patient cohorts, increased surveillance of HIT is necessary.

No relevant conflicts of interest to declare.