title: Evaluating heparin-induced thrombocytopenia: the old and the new.
abstract: Heparin-induced thrombocytopenia (HIT) is a rare but potentially serious complication of heparin use. Prompt diagnosis is crucial and requires the integration of clinical assessment and laboratory testing. Pretest clinical scoring systems (i.e., 4 Ts) have been established. Immunoassays can detect the presence of antibodies directed toward heparin-platelet factor 4 (H-PF4) complexes, but provide no information about their ability to activate platelets. A low clinical score, when combined with a negative immunoassay result obviates the need for further testing. However, immunoassays and 4 Ts scores have only modest specificity. Functional testing (serotonin release assay or heparin-induced platelet activation) remain important in confirming the presence of pathogenic H-PF4 antibodies, but are technically demanding to perform and limited in guiding clinical decisions in the acute setting. This review evaluates current immuno- and functional assays available in the laboratory diagnosis of HIT, and describes recent attempts to improve the specificity of enzyme immunoassays, including adopting an immunoglobulin G-specific assay and raising the optical density value cutoff for a positive result. The importance of donor selection and newer functional assays, including flow cytometry-based assays, are also discussed. A current approach to integrating clinical scoring, immunoassays, and functional testing for HIT is also outlined.
authors.affiliation: Northern Blood Research Centre, Kolling Institute, University of Sydney, Sydney, Australia.
authors.forename: Chee Wee
authors.initials: CW
authors.lastname: Tan
authors.forename: Christopher Morice
authors.initials: CM
authors.lastname: Ward
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Morel-Kopp
mesh_terms: D000906:Antibodies / Q000097:blood; D001792:Blood Platelets / Q000276:immunology; D019411:Clinical Laboratory Techniques / Q000379:methods; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D006493:Heparin / Q000009:adverse effects* / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood / Q000276:immunology; D010974:Platelet Aggregation; D010976:Platelet Count; D010978:Platelet Factor 4 / Q000276:immunology; D012680:Sensitivity and Specificity; D012701:Serotonin; D013921:Thrombocytopenia / Q000139:chemically induced* / Q000175:diagnosis
chemical_list: D000906:Antibodies; D007074:Immunoglobulin G; D012701:Serotonin; D010978:Platelet Factor 4; D006493:Heparin