Strategies for the management of suspected heparin-induced thrombocytopenia: a cost-effectiveness analysis.

BACKGROUND Heparin-induced thrombocytopenia (HIT) is a rare but serious complication of heparin therapy. The diagnosis of HIT is difficult because its signs are non-specific and the heparin-platelet factor 4 (PF4) antibody test used to confirm the diagnosis is imprecise. Drugs used to treat HIT are costly and may carry an increased risk of bleeding. OBJECTIVE To evaluate the cost effectiveness, from a societal perspective, of four treatment approaches for patients with suspected HIT within a US critical care setting. METHODS A decision-tree was constructed for the management of a hypothetical cohort of critical care patients with possible evidence of HIT. The management strategies were: (i) no antibody testing, continue heparin (No Test and Wait); (ii) antibody testing, continue heparin while test results pending (Test and Wait); (iii) antibody testing and switch to a direct thrombin inhibitor (DTI) while test results pending (Test and Switch); and (iv) no antibody testing but switch to a DTI (No Test and Switch). We used argatroban as the DTI in our analysis. The outcomes were direct medical costs ($US; 2004 values), QALYs and incremental cost-effectiveness ratios (ICERs). RESULTS Assuming an HIT prevalence of 3%, relative to less costly strategies, ordering an antibody test and switching patients to argatroban if the result was positive (Test and Wait) had an ICER of $US163 396/QALY. Pre-emptive switching to argatroban without antibody testing (No Test and Switch) was the most effective strategy but had an ICER of >$US1 million/QALY relative to the Test and Switch option. These results were highly sensitive to HIT prevalence among patients presenting with thrombocytopenia. Assuming a willingness to pay of $US50 000 per QALY, the Test and Wait strategy became cost effective when the prior probability of HIT was 8%. At a prior probability of 12%, Test and Switch was cost effective, and at probabilities of HIT in the 60-75% range, No Test and Switch was cost effective. In two-way analysis, the probability of developing a thrombotic event was a key driver of treatment choice at specific HIT probabilities. CONCLUSIONS Testing for HIT in all typical critical care patients with thrombocytopenia is unlikely to represent a cost-effective management strategy. With increasing probability of HIT, strategies that include testing and a more rapid switch to a DTI appear more desirable. Accurate clinical judgment of the prior probability of HIT has a critical influence on the cost-effective management of HIT.