High Rates of Venous Thromboembolism Prophylaxis Did Not Increase the Incidence of Heparin-Induced Thrombocytopenia

Background: Venous thromboembolism (VTE) prophylaxis is recommended for most hospitalized patients. At a 505-bed urban academic medical center, the rate of VTE prophylaxis recently increased from 50%-55% to > 95% of eligible patients. Heparin-induced thrombocytopenia (HIT) is a potentially devastating, but rare, reaction to medications commonly used for VTE prophylaxis. Methods: Patients were identified who were tested for HIT, treated with direct thrombin inhibitors (DTIs), or received International Classification of Diseases, 9th Revision codes consistent with HIT ("suspected HIT") from January 2005 through April 2008. Two physicians classified each patient as having confirmed, possible, or excluded HIT on the basis of laboratory testing, final diagnosis, and clinical course. The rate of suspected and confirmed HIT during the latter two years was compared to rates during the first (reference) year of the project. Results: Some 430 unique patients had received HIT testing or DTI therapy for possible HIT. Thirteen cases of confirmed HIT were identified, of which 7 were due to treatment at the institution and 2 occurred while on VTE prophylaxis. HIT was confirmed in 0.02% of hospital admissions and only 3% of patients initially tested or treated for HIT. Rates of suspected and confirmed HIT did not change during the study period (Risk Ratios [95% confidence intervals] 0.976 [0.77-1.23] and 1.09 [0.39-2.99]). Conclusions: Optimizing the VTE prophylaxis rate to > 95% of eligible patients at a single academic institution did not cause an increase in the rate of HIT. Concerns about HIT should not limit implementation of VTE prophylaxis protocols. HIT surveillance in patients on VTE prophylaxis may have a very low yield.