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How to Report HIT ELISA Results

Here is an interesting question from Dr. Michael D. Blechner of the University of Kentucky:

First I would like to compliment you on a great web site; an extremely valuable resource for myself as well as our residents. Second, I would love for you to do a followup “Quick Question” to evaluate how folks are reporting out and interpreting heparin dependent antibody test results. We use the GTI assay and stick with their recommended cutoff, OD >0.400. As you may know this assay has a confirmatory step after the addition of heparin. We report out positive, negative or equivocal (OD > 0.400 but not confirmed with heparin). We do not report out the ODs. I would be very interested to know who is reporting out the ODs and if folks have added any interpretive categories and/or interpretive comments; for instance, weak positive versus strong positive. The GTI cutoff of 0.400 makes for a pretty sensitive assay. It’s the resulting poor specificity that plagues us when physicians try to rely too heavily on this assay for diagnosis of HIT. Thanks.

Mike Blechner

Michael D. Blechner, MD
Assistant Professor, Pathology & Laboratory Medicine
Director, Pathology Informatics
Director, Coagulation Laboratory
University of Kentucky Medical Center
Lexington, KY

Hello, Dr. Blechner.

Thank you for the compliment and the question. On Monday we will post a “Quick Question” based on your discussion. Because part of your question is open-ended, I want to encourage visitors to add comments to this posting or to send me an e-mail with your answer, which I will post as a follow-up blog.

Your question provides a nice coincidence. Dr. Marisa B. Marques of the University of Alabama at Birmingham Hospital led a discussion of HIT testing last week at our Precision BioLogic Roundtable. She conducted an information-laden data review of the current GTI PF4 IgG/M/A kit with their new PF4 IgG kit, serotonin release assays (SRA) provided by Dr. Jeffery Dlott at Quest Diagnostics, and the 4T clinical and platelet count rating system.

Her data provoked a lively discussion of clinical efficacy among the participants, Drs Adcock-Funk, Kottke-Marchant, and Olson. She will be posting a “guest blog” summarizing her presentation next  week. Geo

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