Over-testing for heparin induced thrombocytopenia in hospitalized patients

Abstract

Heparin induced thrombocytopenia (HIT) is a pro-thrombotic and potentially fatal complication of heparin therapy. Its diagnosis rests on high clinical probability and the laboratory demonstration of anti-PF4/heparin antibodies. The high prevalence of thrombocytopenia in hospitalized patients and the high sensitivity but low specificity of immunoassays for HIT antibodies can lead to over-testing and over-diagnosis. We conducted a study to review HIT screening practices in a tertiary care setting. We reviewed 63 consecutive patients undergoing testing for anti-PF4/heparin antibodies over 3 months. Pre-test probability for HIT was calculated using the 4T score. Sixty three patients underwent testing for anti-PF4/heparin antibodies. Twenty one had been admitted for cardiovascular surgery, 5 for other surgery and 35 for non-surgical indications. Twenty nine patients (46 %) had low pre- test probability, twenty three (36.5 %) had intermediate probability, and eleven (17.4 %) had high pre-test probability of having HIT. Anti-PF4/heparin ELISA was positive in 8 of 63 patients. SRA was ordered for 16 patients and was positive in 5. Only five patients were diagnosed and treated for HIT. Over-testing for HIT is highly prevalent in a tertiary care setting. This increases cost and exposes patients to expensive anti-coagulation with its attendant risk of hemorrhage. The 4Ts score has been shown to have high sensitivity and may be used to rule out HIT in most situations, although its utility depends on subjective analysis. Consistently applying this in practice could minimize over-testing and facilitate safer, cost-effective care.

False positive immunoassay for heparin-induced thrombocytopenia in the presence of monoclonal gammopathy: a case report

“…Moreover, Alpert et al found the prevalence of heparin/PF4 antibodies ranging between 4 and 15% in patients with antiphospholipid syndrome and systemic lupus erythematosus, respectively, often in the absence of clinical HIT or recent heparin exposure ( 23 ). As previous cases demonstrate, leaning on positive immunoassay alone can lead to a wrong suspicion about HIT and potential use of other anticoagulant drugs that can cause bleeding and additional healthcare costs ( 24 - 26 ). For that and similar reasons samples positive for HIT-autoantibodies in immunoassays should be evaluated by the functional tests.…”

HIT or Miss

“…4 The 4T score has been validated in numerous adult studies and a low 4T score (1 to 3) has a 99.8% negative predictive value. Given the ready availability of high-sensitivity, low-specificity H-PF4 antibody assays, it is not surprising that HIT is commonly suspected and tested for.…”

Novel method using rotational thromboelastography analysis for intraoperative management of device patient with heparin-induced thrombocytopenia

“…Heparin-induced thrombocytopenia (HIT) is an immune-mediated prothrombotic disease in response to previous heparin exposure [1] Direct thrombin inhibitors (DTIs) are suitable candidates for the prophylaxis of thrombosis in patients with HIT [2][3][4][5][6]. Bivalirudin, a common DTI, can be considered as a therapeutic alternative to heparin [3,[5][6][7].…”