title: 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.
abstract: 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.
authors.affiliation: Department of Laboratory Medicine, Kantonsspital, Aarau, Switzerland.
authors.forename: Lorenz
authors.initials: L
authors.lastname: Risch
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bertschmann
authors.forename: Ingmar A F M
authors.initials: IA
authors.lastname: Heijnen
authors.forename: Andreas R
authors.initials: AR
authors.lastname: Huber
mesh_terms: D000368:Aged; D001323:Autoantibodies / Q000097:blood*; D013504:Cardiovascular Surgical Procedures; D005260:Female; D005782:Gels; D006493:Heparin / Q000276:immunology*; D006801:Humans; D007118:Immunoassay / Q000379:methods* / Q000592:standards; D008297:Male; D008875:Middle Aged; D010978:Platelet Factor 4 / Q000276:immunology*; D011183:Postoperative Complications / Q000139:chemically induced / Q000175:diagnosis; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013927:Thrombosis / Q000139:chemically induced / Q000175:diagnosis* / Q000276:immunology; D013997:Time Factors
chemical_list: D001323:Autoantibodies; D005782:Gels; D010978:Platelet Factor 4; D006493:Heparin