ORIGINAL ARTICLESMicroparticle counts in platelet-rich and platelet-free plasma, effect of centrifugation and sample-processing protocolsChandler, Wayne L.Author Information Department of Pathology and Genomic Medicine, The Methodist Hospital, Houston, Texas, USA Correspondence to Wayne L. Chandler, MD, Methodist Pathology Associates, 6565 Fannin, Suite B-490, Houston, TX 77030, USATel: +1 713 441 9976; fax: +1 713 441 3489; e-mail: firstname.lastname@example.org Received 9 March, 2012 Revised 26 June, 2012 Accepted 3 August, 2012 Blood Coagulation & Fibrinolysis: March 2013 - Volume 24 - Issue 2 - p 125-132 doi: 10.1097/MBC.0b013e32835a0824 Buy Metrics Abstract This study provides the first estimates of microparticle numbers in platelet-rich plasma (PRP) from normal individuals, closer to in-vivo levels, using higher-resolution flow cytometry. We measured platelet (CD41+) and annexin V+ microparticles in fresh and frozen aliquots of PRP, platelet-poor plasma, platelet-free plasma (PFP), and microparticles isolated by high-speed centrifugation. PRP from healthy individuals contained 730 000/μl total microparticles based on light-scattering measurements. A median of 27 000/μl microparticles in PRP were of platelet origin and 120 000/μl annexin V+, and of these, 24 000/μl were dual-positive procoagulant platelet microparticles. Double centrifugation of PRP removed 99% of platelets, but also 80% of annexin V+ CD41+, 93% of annexin V+ CD41−, and 58% of annexin V− CD41+ microparticles. Loss of microparticles with centrifugation varied from individual to individual. Microparticle counts after isolation by centrifugation and double washing were not significantly different than counts in the original PFP sample, but lower than in PRP. Freeze-thawing of PFP had no effect on platelet microparticle counts, but slightly increased annexin V+, CD41− counts. Freeze-thawing of isolated washed microparticles resulted in a 30–50% increase in annexin V+ microparticles. PRP contains large numbers of cellular microparticles, including platelet and annexin V+ microparticles, which are lost to varying degrees when PRP is double centrifuged to remove platelets. Microparticles remaining in PFP can be recovered by high-speed centrifugation without loss compared to the original PFP sample. Freeze-thawing has variable effects on microparticle counts depending on the sample preparation used. © 2013 Lippincott Williams & Wilkins, Inc.