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Platelet Satellitism

Here’s a March 11, 2024 message from Erika Knuckles, Hematology Supervisor, Phelps Health. “Good Morning George, I was consulting ‘Mr. Google’ to see if I could find any information on what would cause patients to form platelet clumps in both EDTA and sodium citrate. We excluded the collection process. diseases, and medication. I thought you might be able to direct me. We have had a couple of patients whose sodium citrate did not resolve the issue. Sometimes, a gentle vortex will help. Thanks!

My reply: Hello, Erika, and thank you for your email. While platelet clumping is most often associated with inadequate specimen mixing, in your case it appears to be platelet satellitism [PS]. PS occurs in about 1 in 10,000 specimens when EDTA exposes platelet membrane “cryptoantigens” to which autoantibodies become attached and then bind the platelets to neutrophils [PMNs], to each other, and sometimes to monocytes and even lymphocytes. PS has no direct clinical consequence except that the resultant pseudo-thrombocytopenia can lead to unnecessary platelet concentrate transfusions unless the lab staff observes the discrepancy.

I’ve had the experience of PS appearing in both EDTA and citrate specimens and reverted to collecting a specimen in a lithium heparin tube, which can yield an accurate platelet count but causes poor cellular morphology. You need no correction factor as the heparin is coated dry on the inner surface of the collection device.

Below is a reference to a copyrighted case study that suggests using gentle vortexing to release platelets from PMNs and break up clumps, however, the authors caution that the resulting platelet count and differential may not be accurate.

Tantanate C. Vortex mixing to alleviate pseudothrombocytopenia in a blood specimen with platelet satellitism and platelet clumps. Clin Chem Lab Med. 2020 Nov 19;59(5):e189-e191. doi: 10.1515/cclm-2020-1432. PMID: 33554527.

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