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Platelet Counts from Citrate Tubes

Here is some correspondence between Estelle Ninnemann at ACL Laboratories, and Dennis Ernst, at the Center for Phlebotomy Education, Inc.

From Estelle, “In our laboratory, phlebotomists collect sodium citrate (blue top) tubes when a patient is known to have a history of platelet clumping. The sample is collected and sent with the lavender top tube for hematology testing. This does not cause an issue in our hospital settings as testing is done on site.  Both tubes are transported room temperature and testing is completed in a timely manner. What is the best practice associated with transporting the blue top tube for platelet counts when the sample needs to be analyzed at a different location? Should the blue top tube be maintained at room temperature or can this be refrigerated during transport?  I could not find specific references in the manufacturer’s insert, CLSI, or from our hematology vendor.”

Here is Dennis’s response:

Estelle, nice to hear from you.

I’m of the understanding platelets are stable at room temperature for 24 hours in EDTA tubes. I don’t know that they’d be any less stable in sodium citrate tubes. But I want to send this question to my go-to guy for coagulation stumpers like this. George Fritsma is a good friend and the purveyor of The Fritsma Factor, an online forum for questions just like this. You should sign up and make it your place to go for authoritative answers on coag. George, what is your take on Estelle’s question? Thanks, George.

Here is George’s response:

Hello, Dennis and Estelle, refrigeration appears to precipitate large von Willebrand factor multimers, which could tend to activate stored platelets. Also, we’ve for many years stored donor platelet concentrate at 22°C with the understanding that storage at 4°C causes platelets to lose their energy-dependent normal shape and to clump.

Just to mess us up, there exist a handful of recent articles in Transfusion that seem to indicate less platelet lesion at refrigerator temperatures than room temperature; for example Bynum JA, Meledeo MA, Getz TM, et al, Bioenergetic profiling of platelet mitochondria during storage: 4°C storage extends platelet mitochondrial function and viability.Transfusion. 2016;56 Suppl 1:S76–84. These publications seem to flout conventional wisdom, so maybe the rules will change in the future.

However, these experiments are performed on CPD storage platelets, which may not generalize to citrate platelets, so at least for now, I recommend that Estelle’s facility store both the EDTA and citrate specimens at room temperature and ensure the counts are performed within 24 hours.

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