Comparing Screening Techniques for the Identification of HIT Antibodies

Claire North, Haematology

North C, Holtom P, Smith N

Presented By: Claire North

Heparin induced thrombocytopenia (HIT) is a major complication of heparin therapy. HIT is a transient, drug induced autoimmune disorder. The pathogenesis involves the formation of multimolecular complexes between heparin, PF4 and antibodies generated against heparin: PF4 complex which acts as an antigen. This is turn leads to activation of platelets, monocytes and vascular endothelium to the generation of thrombin. HIT typically presents 5-10 days after the initial exposure to heparin with a decrease in the platelet count by 30-50%. It is one of the most important drug-dependent immuno-haematological disorders. The pathological role of heparin-induced antibodies in causing HIT means that the laboratory plays an important function in supporting or refuting the diagnosis. A quick reliable determination of the presence of the anti-heparin and platelet factor 4 antibodies needs to established and implemented as an in-house test.

There are a number of different techniques that are used to determine HIT. Three techniques have been tried and tested with the anticipation that one technique could be established into the working environment at the haematology department. The techniques used are flow cytometry, AESULISA HIT II ELISA kit and DiaMed ID-PaGIA heparin/PF4 antibody test.

Over the course of the project, 15 patient samples of known HIT status from the National Blood Service (NBS) were collected which were tested on all three techniques. All three techniques were set up and verified with controls. Results from all three techniques were compared to the results obtained from the NBS and showed conflicting results. It was found that samples stored in the freezer at -40ºC lost their sensitivity and could no be tested on the flow cytometer or DiaMed gel cards. Only fresh serum samples could be used. This restricted the results obtained.

There is not one technique that can be established for use in the laboratory. Future requests for HIT screening will still be tested on all three techniques to obtain further results and comparisons.