The beneficial effects of the combined methods in investigating heparin-induced thrombocytopenia

Introduction

Heparin-induced thrombocytopenia (HIT) type II is a serious side effect of unfractionated heparin, and to a lesser extent of low molecular weight heparins. It is mediated through an immunological mechanism and leads to platelet aggregation. The occurrence of HIT varies between 1% and 5% of patients receiving heparin while a substantial fraction of them develops thrombosis (HITT). Therefore, the rapid and accurate confirmation of HIT is a necessity. The laboratory assays available for the diagnosis of HIT are based on the detection of HIT antibodies or on the consequences of platelet activation (functional methods). The purpose of the present study was to improve HIT recognition by the combination of functional and antibody determination assays.

Patients and methods

Fifty-three patients who presented thrombocytopenia while receiving UFH or LMWH participated in the study. A positive control group consisting of 15 patients known to suffer from HIT/HITT was used. Moreover, 19 healthy donors never exposed to heparin also participated as negative controls. The antibody determination was performed using commercially available ELISA kits. In the functional assays, heparin-induced platelet activation/aggregation (HIPA) and a flow cytometric technique for the detection of platelet microparticles released (platelet microparticle assay) were included.

Results

None of the negative control individuals were positive in any applied method. In contrast, all the participants of the positive control group were found positive in all the applied methods. No HIT was detected in 10 patients, seven of whom were pregnant at different gestational ages. The remaining 43 thrombocytopenic patients were positive in HIPA and 39 of them were also positive in the platelet microparticle assay. Out of these 39 patients, only 16 were positive in the ELISA assay.

Conclusion

In comparison with the HIT-positive control group it was found that: a 92% agreement existed between the HIPA and the platelet microparticle assays; and the positive results in the ELISA were significantly lower than in the functional methods, indicating perhaps a lower sensitivity (41% agreement with the flow cytometric method and 32% with the HIPA). Therefore, the combination of functional and antibody detection assays is a necessity for the HIT recognition since both could give pseudo-positive or pseudo-negative results.