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A PTT Discrepancy

I received this interesting question on Friday, October 3 from Priscilla Koernert:

Hi George,
I ran across your site while researching a method discrepancy regarding PTT results. We are currently using Stago Compacts obtained a result of 100.9 on a non-heparinized patient.  The physician subsequently ordered further coag testing which we send over to the local university hospital lab.  They perform their coags using the Beckman ACL TOP.  Their result differed from ours significantly, it was 26.6!  This patient was post-surgery, also had an elevated FVIII and fibrinogen.  Further studies were suspicious for lupus anticoagulant with follow-up testing recommended.  What are your thoughts on the discrepancy?  Is it a result of different methodologies?  Any insight you can provide will be much appreciated.
Thank you.

Hi, Priscilla, thank you for your question. I’ll start by assuming your Stago PTT and University’s ACL PTT were performed using aliquots from the same specimen. I’d suspect the patient has specimen contains an inhibitor that prolongs the Stago reagent but not the ACL’s. My suspicion is supported by the possible presence of a lupus anticoagulant. I grant you that 100.9 Vs. 26.6 seconds is a profound difference, however, and I’d love to hear from others who have experience with these two reagents, particularly the scientific people from Stago and Beckman-Coulter (IL).

The elevated FVIII and fibrinogen may just reflect tissue damage following surgery. The elevated VIII can slightly shorten a PTT and render it less sensitive to heparin therapy, however it can’t account for this great a difference. Let’s see what our participants think. Geo

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