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Aim: We assessed reproducibility of endothelial microparticles (EMPs) enumeration among youth. Methods & results: Four microparticle (MP) indices – total MP per microliter platelet free plasma (PFP), total EMPs per microliter PFP, percent activated EMPs and percent lactadherin positive (LACT[+]) of total EMPs – were measured at two visits (baseline and 7 ± 3 days follow-up) to determine reproducibility overall and by obesity status. We examined CD31+ or CD144+ with CD41-EMP events of size 0.3–1.0 μm. No statistically significant differences were observed between visits for any of the four MP indices. The within-participant and between-participant coefficient of variation was acceptable (range: 1.13–2.37) with good intraclass-correlation coefficient for all indices except total MP per microliter (range: 0.10–1.00). Conclusion: Total EMPs per microliter PFP, percent-activated EMPs and percent LACT(+) of total EMPs are reproducible among youth.

Introduction: We examined the reproducibility of circulating endothelial cells (CEC) enumeration and activation among youth. Materials and methods: CECs from 151 youth were measured at baseline and 1 week follow-up. Enumeration of CEC in fresh whole blood was determined by direct assessment of buffy coat smears (CD146+ nucleated cells) and activated CEC (%VCAM-1 expression) was determined after immunomagnetic enrichment and co-staining of nuclei, plus positivity for P1H12 and VCAM-1. Results: No statistically significant difference in CEC enumeration (1.2 ± 2.5 vs 1.3 ± 2.2 CEC/milliliter of whole blood, p = 0.745) or activated CEC (57.1 ± 24.4 vs 58.0 ± 21.3 %VCAM-1, p = 0.592) between baseline and 1 week follow-up. Conclusion: On a cohort basis, CEC enumeration and activation are reproducible in youth. Relatively high individual biological variability may limit its clinical utility.