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Quick Question: HIT Testing

Our April Quick Question was “How do you test for heparin-induced thrombocytopenia (HIT)?”
Here are the compiled answers:
a. Platelet count only: 4 (8%)
b. Platelet count and immunoassay: 22 (45%)
c. Platelet count and heparin-induced platelet aggregation (HIPA): 10 (20%)
d. Platelet count and serotonin release assay (SRA): 2 (4%)
e. Platelet count, immunoassay, and functional release assay, either HIPA or SRA: 11 (22%)
This question has one weakness; it fails to define carefully what form of HIPA is asked for. In my experience, a standard platelet aggregometry assay that uses heparin as its agonist should work in theory, however is insensitive and likely to miss a significant number of HIT antibodies. The washed platelet suspension aggregometry assay may be more sensitive, though it is technically demanding.
Of course, the SRA is the reference method, but is available from relatively few reference labs, owing to the radioactive isotope. We send ours to Dr. Ted Warkentin’s lab at McMaster University in Hamilton, Ontario.
Our current best laboratory/clinical approach to the rapid diagnosis of emergent HIT is Dr. Warkentin’s “4T” system: Thrombocytopenia (acute); Timing of platelet count fall;Thrombosis or other sequelae and oTher causes for thrombocytopenia.
I look forward to one of our distributors developing a rapid and specific immunoassay, as our current enzyme immunoassay procedures are too slow for a stat diagnosis, though they are helpful in providing an initial confirmation of the diagnosis. Enzyme immunoassays have a high false positive rate, especially in coronary artery bypass surgery; this is another weakness.
I hope we get comments from our participants, as there is a lot to say about HIT testing.

Comments (2)
Jun 3, 2010 3:17am

Hi, Joe. I’ve heard several users say they had abandoned the
Hi, Joe. I’ve heard several users say they had abandoned the Akers PIFA Heparin/PF4 rapid assay because it is too hard to read the blue end-point. I see that Akers has a second-generation implement they claim provides clearer results; that must be what you are using. To be fair to Akers, please give us more detail on how it works for you. Geo.

May 17, 2010 5:22pm

George, what about the PIFA rapid assay? I really don’t con
George, what about the PIFA rapid assay? I really don’t consider it an immunoassay, I’m assuming you mean an ELISA test. We use the PIFA device along with the platelet count and it seems to work well in a screening situation.

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