Prospective evaluation of two specific IgG immunoassays (HemosIL(R) AcuStar HIT-IgG and HAT45G(R)) for the diagnosis of heparin-induced thrombocytopenia: A Bayesian approach

Introduction The accurate diagnosis of heparin-induced thrombocytopenia (HIT) is essential to ensure adequate treatment and prevent complications. First step diagnosis test are immunoassays including enzyme-linked immunosorbent assays (ELISAs) and rapid immunoassays. Methods Using a Bayesian approach, we prospectively evaluated the performance of the IgG PF4/polyvinylsulfonate ELISA and a chemiluminescent immunoassay (CLIA), which are specific for IgG and use the same antigenic target to detect HIT antibodies. Results One hundred and eighty-four 184 consecutive patients with an intermediate (n = 159) or high (n = 25) clinical pretest probability of HIT based on the 4Ts score or platelet pattern were included. Both immunoassays (IAs) were performed on all 184 samples, and definite HIT was confirmed with a positive serotonin release assay in 29 patients (12.7%). The sensitivity (Ss) and negative predictive value (NPV) of ELISA were excellent (100%) allowing HIT to be excluded with good confidence when the test was negative. In addition, the Ss and NPV of the CLIA equalled 93.1% and 98.6%, respectively, as it was negative in two definite HIT. When the CLIA was negative, the post-test probability of HIT was 0.7% in case of intermediate risk. Although there was excellent agreement between CLIA and ELISA results, the quantitative values provided by the two IAs were not correlated. Conclusion AcuStar HIT(R) detects more than 90% of HIT, as do all rapid IAs, and appears to be a good tool for excluding HIT when the pretest probability is intermediate. A chemiluminescent signal higher than 10 IU/mL is highly predictive of definite HIT with a PPV of 100%.