A differentiated approach to assess the diagnostic usefulness of a rapid particle gel immunoassay for the detection of antibodies against heparin-platelet factor 4 in cardiac surgery patients

Enzyme-linked immunosorbent assay (ELISA) methods have shown to be of a low specificity for confirming heparin-induced thrombocytopenia (HIT) in cardiac surgery patients. In other patient collectives, a new antigen test [ID-HPF4 Particle Gel Immuno Assay (PaGIA); Diamed, Cressier sur Morat, Switzerland] was recently reported to exhibit a better specificity than the ELISA. Since a more specific test would serve as a useful tool when diagnosing HIT, a prospective study was carried out to elucidate the specificity and diagnostic usefulness of PaGIA in cardiac surgical patients. As assessed in cardiac surgery patients without HIT, the proportion of PaGIA-positive samples was lowest at baseline (16%; 13/74), increasing to 31% (19/61) at postoperative days 5–9 (P = 0.06) and 69% (29/42) at postoperative days 10–18 (P < 0.001 versus postoperative days 5–9). The respective proportions in an ELISA (HPF4 ELISA; Stago, Asnières sur Seine, France) were lower. Because the prevalence of antibody positivity increases during the postoperative course, a differentiated mathematical model was used to assess predictive values and likelihood ratios (LR) of the PaGIA at three different phases of hospitalization. Calculating LR revealed –LR to be 0.07 at baseline, 0.09 during postoperative days 5–9, and 0.19 during postoperative days 10–18, while +LR were 5.9 at baseline, 3.0 during postoperative days 5–9, and 1.4 during postoperative days 10–18. Thus, in cardiac surgery patients, the PaGIA can be regarded as a useful tool in excluding rapid onset and typical onset of HIT, and further provides valuable information in the confirmation of rapid onset of HIT. Using a differentiated approach for calculation of predictive values and LR, the present study demonstrates that PaGIA, despite a lower specificity than the employed ELISA, in some situations is a valuable tool when diagnosing HIT in cardiac surgery patients.