From Tiffany Jones, Orlando Health: I was wondering if you could clarify for me why we can’t use a blue citrate tube for a platelet count after it has been spun once. Are there any studies to back up this reason? My facility seems to get a fair amount of patients displaying EDTA-induced platelet clumping and we resort to asking for a recollect on the patient because if a blue top had been drawn, in all likelihood it was spun in the coagulation department. It also gets a little trickier when the patient is an outpatient draw. Thank you for your time!
Hello, Tiffany, thanks for a provocative question. The short answer is no, having done a literature search, I find there are no published studies that indicate platelet counts from centrifuged and subsequently resuspended citrate whole blood specimens are either valid or unreliable. We rely on expert opinion, which assumes that centrifuged platelets are likely to become activated and clumped. The clumped platelets are unlikely to resuspend evenly. The question is not addressed in the relevant and most recently published CLSI documents, H3 and H21, Procedures for the Collection of Blood Specimens by Venipuncture, and Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays and Molecular Hemostasis Assays, respectively.
I’ve forwarded your question to two specimen management experts and hope to get additional responses from them. Meanwhile, it may be interesting to run a simple platelet count study in your own laboratory to find out what happens to the platelet count from a resuspended tube. Check back soon for some additional responses.
I concur with all statements
I concur with all statements ahead of me in the queue. If you spin the citrate tube you activate the platelets–try doing a PFA on spun and remixed tubes and you will get flow obstructions due to platelet aggregates. It’s a good teaching tool. So, doing a blood count after the spin/remixing will lead to a false low platelet count. Can’t recall a publication on this, but many of us have done this by trial and error and it checks out. Don’t spin; remix and count.
Dave McGlasson writes, “most
Dave McGlasson writes, “most of the evidence I can give you is anecdotal on this issue.” When blood is centrifuged, platelets are activated to some extent. See the following article: McGlasson DL, Fritsma GA. Whole blood platelet aggregometry and platelet function testing. Semin Thromb Hemost 2009;35:168–80. In this article we cite why whole blood should be used for platelet functional testing instead of centrifuged citrated blood.
In personal experience using a variety of devices for measuring platelet function I can offer this advice. Platelets will aggregate when centrifuged, creating a falsely lower number of platelets due to small platelet aggregates. When I first started working with the PFA-100 we looked at citrated whole blood vs centrifuged and then remixed the spun citrated blood for three minutes and found the closure time much higher in the centrifuged specimens. When using the PlateletWorks system with Helena we found that the citrated whole blood vs the EDTA levels were very different when the citrated blood was allowed to just be kept at room temperature and then inverted and have the platelets re-analyzed. We found clumping with lower platelet counts. Hope this helps.
Hi, Tiffany. It’s an
Hi, Tiffany. It’s an interesting question, but I, too, sense this technique would yield unreliable results. Resuspension would have to be verified and controlled. There’s no reliable evidence this technique wouldn’t alter test results. While I agree there needs to be valid studies conducted and published on this, I’d be surprised if it would be reliable under all patient and processing variables. Perhaps the safer approach is to draw a citrate tube on those known patients with EDTA-induced clumping exclusively for the platelet count. That won’t solve every problem, but it will help with those you know about. Good luck.