Here is a Paul Riley, PhD follow up to Diane Treadway’s discussion and follow-up comment comparing the ISTAT INR to the central lab plasma-based PT/INR.
From Dr. Riley, Stago-US. I don’t understand what is happening with the bivalirudin interference. According to Gosselin et al. (below) there should be minimal effect on the Stago PT (see fig. 1M and N) from bivalirudin interference and we have a heparin neutralizer in the reagent as well. However, there was a great deal of reagent variability and we also don’t know the true level of the bivalirudin in the patient nor do we know the renal clearance, which greatly affects the drug half life. I don’t see anything in the ISTAT package insert regarding bivalirudin interference. The bivalirudin half life is very short, only 25 minutes. It sounds like from Ms. Treadway’s comments on the post that the 14:30 sample also had a main lab INR done simultaneously and the INR was 2.2. However, if the main lab INR was not performed at that time, but only at 1155, then maybe it’s possible the bivalirudin had cleared by that time, again assuming the bivalirudin had been stopped, but it’s hard to tell also from the comments. (So I’m still confused.)
Gosselin RC, Danger WE, King JH, et al. Effect of direct thrombin inhibitors, bivalirudin, lepirudin, and argatroban, on prothrombin time and INR values. Am J Clin Pathol 2004;124:593–9.
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