Case 1 – update 2

Hello all. Thank you for your comments on investigations for HIT. As mentioned by a number of contributers there are a number of tests available when investigating a patient for possible HIT. These are summarised in a comment from a Newcastle BMS (you may want to check with your local lab as to the tests they use).

Back to the case…The patient is tested, initially using a rapid gel agglutination assay. This is positive. However this is a test with a good negative predictive value but poor positive predictive value due to a lack of specificity. Therefore further testing was performed by ELISA and was also positive.


What anticoagulant would do you use? How do you monitor this and what problems do you encounter?

Comments on HIT screening

An initial HIT screen using a rapid gel particle agglutination method (Biorad/Diamed) in which polymer particles coated with heparin/PF4 are mixed with patient serum in a small gel ID card. After 5 minute incubation the card is centrifuged for 10 min and the results interpreted visually. In a HIT positive result the particles agglutinate and remain on the top of the gel, negative test results in particles being centrifuged to the bottom of the gel.
We also have a second line test Enzyme Immuno assay ELISA IgG (GTI) which we perform on any HIT screen tests which are positive which takes about 2 hours to perform. The ELISA test uses micro plate strips coated with PF4-PVS which will bind with any HIT antibody present, a second antibody is added coated with a marker which binds to the HIT PF4-PVS complex, substrate is added and the marker produces a colour change proportional to the amount of HIT IgG antibody bound to the micro plate well, the OD(optical density) is determined using a micro plate spectrophotometer reader.   The second confirmation part of the GTI ELISA assay utilises heparin to determine if the positive result is inhibited by heparin – to make the test more specific for HIT antibodies.

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