Rapid exclusion or confirmation of heparin-induced thrombocytopenia: a single-centre experience with 1291 patients

Background The current gold-standard for diagnosing heparin-induced thrombocytopenia is the detection of platelet-activating antibodies by means of functional assays which, being time consuming and not widely available, are not suited for guiding acute treatment decisions. The objective of our study was to assess the ability of more rapid immunoassays to predict the presence of functionally relevant anti-platelet factor 4/heparin-antibodies. Design and Methods We analysed 1291 out of 1383 (93.4%) patients consecutively evaluated for suspected heparin-induced thrombocytopenia at our institution. Clinical pretest probability was defined by the 4T-score. Anti-platelet factor 4/heparinantibodies were measured with three immunoassays (ID-H/PF4-PaGIA, Asserachrom-HPIA, and GTI-PF4) and their functional relevance was assessed by a two-point heparin-induced platelet aggregation-test. The performance of the immunoassays was evaluated by receiver operating characteristic analysis. Results Among 1291 patients, 96 (7.4%) had a positive heparin-induced platelet aggregation-test: 7/859 (0.8%) with a low, 50/358 (14.0%) with an intermediate, and 39/74 (52.7%) with a high 4T-score. Receiver operating characteristics analysis indicated that best immunoassays’ thresholds for predicting a positive platelet aggregation-test were: Titer ≥4 (ID-H/PF4PaGIA), optical density >0.943 (Asserachrom-HPIA) and >1.367 (GTI-PF4). A 100% negative predictive value was observed at following thresholds: Titer ≤1 (ID-H/PF4-PaGIA), optical density <0.300 (Asserachrom-HPIA) and <0.870 DOI: 10.3324/haematol.2011.048074