I was referred to you by my current professor John Landis. I have a question regarding PT‘s being performed in a reference lab setting.
The laboratory that I work for is essentially a reference lab in that we get samples from the surrounding areas and even different states. We typically receive our samples via a FedEx delivery, and the sample are sometimes exposed to the elements when they shouldn’t be. In the winter I notice quite a bit of fibrin in our samples on our CBCs. We have a bunch of different rejection criteria for the lavender tubes depending on the results and previous histories, but not so much for the blue top tubes. I would imagine that the blue top tubes that we use for our PT/INRs aren’t any different, and the only reason we see fibrin more so in the lavender tubes is because we’re reviewing the slides and checking for clots more often there.
So my overall question is, wouldn’t the fibrin found in the blue tops affect result for the PT/INR since some of the clotting factors are being consumed in the process? I was curious enough about it to pull some statistics from our LIS and found that the average PT/INR from a month like January or February wasn’t any different than a month like June. And actually, the mean of all of our individual months are within a few tenths of a second. I suppose that it’s also worth mentioning that we are still in the same lot of reagent currently that we were back in January, so the actual time in seconds should be comparable.
I’m happy that I didn’t find a discrepancy in results, but I would still like to better understanding as to why this is the case. We’ve had a change in leadership in the lab in the recent past and I’ve observed both schools of thought on this, where one supervisor was adamant about checking all blue top tubes for fibrin and rejecting the sample if any amount was found, and the other who was only concerned if the results were critical. I’m actually the one overseeing the department now and I would like to make an informed decision before I decide how I would like our lab to go about this.
I appreciate your time and thoughts, and I look forward to hearing from you, Eric Sutter.
Hello, Eric, and thank you for a timely question. Thank also to Prof. Landis, a long-time colleague and good friend, for referring you to Fritsma Factor. To drop a name, just yesterday I was talking with Dennis Ernst, Center for Phlebotomy Education, about specimen integrity. Dennis says we lack solid standards for specimen transport, though the CLSI GP41 Standard, “Collection of Diagnostic Venous Blood Specimens, 7th Edition,” does provide clear standards for specimen identification and collection and reccomendations for specimen storage. We don’t currently have a way to document elapsed time from collection to testing, nor do we record the temperatures or mechanical agitation the specimens are subjected to in transport, all of which can partially activate platelets and the coagulation cascade and cause hemolysis.
From your data collection, it seems you can trust the integrity of your specimens, though it is important to routinely screen for small clots or fibrin strands. You have a clear advantage when a lavender tube arrives with the blue tube, since you can readily identify fibrin in the blood film. I would tend to side with supervisor #1 who rejects specimens with visible fibrin. We typically assume that fibrin formation indicates coagulation factor consumption, prolonging the PT and PTT, but I’ve also read of instances where partial clotting shortens the PT and PTT, implying that some currently activated factors are lurking in the plasma. This could mean that a PT performed to monitor Coumadin could be factitiously shortened, leading to a dosage change. A near-normal finding could mask a critical condition.
I’ve posted a Quick Question about specimen transport, and will reach out to a few colleagues at reference laboratories for comments. Watch this space for additional responses.