Laboratory Diagnosis of Heparin-Induced Thrombocytopenia

Abstract

The characteristics of the currently available platelet function assays (platelet aggregation, serotonin release, and flow cytometry) and enzyme-linked immunosorbent assays that quantitate antiheparin-platelet factor 4 antibody titers were studied using sera collected from clinically diagnosed heparin-induced thrombocytopenia patients, patients without heparin-induced thrombocytopenia, patients with platelet immune disorders other than heparin-induced thrombocytopenia, and normal individuals. The platelet aggregation assay was less sensitive than the serotonin release assay, which was less sensitive than the enzyme-linked immunosorbent assay (p < 0.001). Yet heparin-induced thrombocytopenia was identified by platelet aggregation assay in cases where the serotonin release assay and/or the enzyme-linked immunosorbent assay were negative. Patients with heparin-induced thrombocytopenia and thrombosis were more often positive than heparin-induced thrombocytopenia patients without thrombosis (p < 0.05). Positive platelet aggregation assay and serotonin release assay results were generally associated with a higher antibody titer; however, a minimum critical titer could not be identified. Over a 30-day period the percentage of positive responses did not change significantly even though clinical symptoms corrected in most heparin-induced thrombocytopenia patients. Multiple testing over several days enhanced the chance of detecting a positive, and combined results of the three assays further enhanced the positive response (p < 0.005). In patients without heparin-induced thrombocytopenia, false-positive results were obtained with the enzyme-linked immunosorbent assay. These data demonstrate that there is no direct correlation between the positive responses of these assays, that clinically positive patients can be missed by all assays, and the presence of antibody alone does not determine clinical heparin-induced thrombocytopenia. With these limitations, the combination of aggregation, serotonin release, and enzyme-linked immunosorbent assay testing with multiple samples offers the best chance of identifying a positive heparin-induced thrombocytopenia patient. Caution is advised for all assays as none is optimal.

Anti-Heparin-Platelet Factor 4 Antibody is a Risk Factor for Vascular Access Obstruction in Patients Undergoing Hemodialysis

“…The most recent tests for heparin-dependent antibodies are based on the recognition that the antibodies are directed against the heparin-platelet factor 4 complex by enzyme immunoassay (3,16). Since this method was more sensitive and easier to perform than conventional platelet function assays such as platelet aggregation, serotonin release, and flow cytometry (17), and immunoassays and functional assays agree in about 80% of cases (18), we applied the method to determine the anti-heparin-platelet factor 4 antibodies in this study. These antibodies, however, are generated only in part of heparin-treated patients, and still only a subgroup of them develop vascular access obstruction.…”

Platelet factor 4/heparin antibody (IgG/M/A) in healthy subjects: a literature analysis of commercial immunoassay results

“…In three of these seven articles, the described assay ultimately served as basis of a commercial assay [12,13,19]. The literature set comprised the remaining 11 articles [10,16,17,[20][21][22][23][24][25][26][27], each of which reported the prevalence of PF4/heparin antibodies in healthy subjects, as assessed by a commercial immunoassay according to manufacturer's directions (Table 1). …”

New laboratory test in flow cytometry for the combined analysis of serologic and cellular parameters in the diagnosis of heparin‐induced thrombocytopenia

“…Moreover, in patients 8 and 12 the thrombotic complications were already present before the initiation of heparin therapy and therefore presumably not due to the development of HIT. Further, patients 10 and 11, who had borderline titers in their positive ELISAs (16,19), had suspected HIT due to a modest decrease in platelet count but subsequently showed no complication related to the formation of thrombi. In these cases, that were not confirmed by clinical evaluation as HIT, ELISA was positive, whereas flow cytometry was not.…”

“…The search for anti-H:PF4 antibodies in the patient's serum by ELISA is generally held as a confirmatory laboratory test that, however, does not influence the clinical decision. This is essentially due first to the fact that several patients develop anti-heparin antibodies during heparin therapy, but only a minor percentage develop clinical HIT; further, H:PF4 ELISA can give false positive results (7,(15)(16)(17)(18). Hence, there is need for a test that, in addition to the serologic detection of antibodies, can reveal their activatory properties.…”