Quantification of RPs, preplatelets, and barbells in human whole blood. Healthy control trisodium citrate–anticoagulated whole blood was labeled immediately after phlebotomy with anti-CD42b BV421 and TO, Mitotracker AF599, or anti-HLA-I APC (n = 5; bar represents 7 μm), and granularity was determined by SCC light. (A) Representative images of preplatelets and barbells with each label are shown. Mean fluorescence intensity (MFI) was normalized to the cellular perimeter. (B) Under the same conditions, citrate blood was labeled with anti-CD61 FITC and CD62p BV421 for 15 minutes at 37°C, %IPF platelets was measured by Sysmex XN1000, and preplatelets and barbells were quantified by ISFC and correlated with IPF (n = 12). (A-B) One-way analysis of variance with Dunnett’s multiple-comparisons test ±1 standard deviation; (B) Pearson’s correlation coefficient. *P < .05; **P < .01; ***P < .001; ****P < .0001.