The Time of Blood Collection Does Not Alter the Composition of Leucocyte-Poor Platelet-Rich Plasma: A Quantitative Analysis of Platelets and Key Regenerative Proteins.

Platelet-rich plasma (PRP) is increasingly used in orthopedics, with its regenerative potential attributed to platelet-derived cytokines and growth factors. However, variability in PRP composition hampers standardization and reproducibility, contributing to inconsistent outcomes. Since platelet counts in whole blood follow circadian rhythms, we investigated whether blood collection time affects PRP composition. Venous blood was collected from 25 healthy individuals at 8:00 a.m., 12:00 p.m., and 4:00 p.m. Whole blood was analyzed, and leukocyte-poor PRP (LP-PRP) was prepared for quantification of erythrocytes, leukocytes, and platelets. Platelets were lysed by freeze-thaw cycles, and protein levels of PDGF-BB, IGF1, HGF, IL6, and IL10 were measured via ELISA. Whole blood exhibited diurnal variation in platelet counts. In contrast, LP-PRP was consistently depleted of leukocytes and erythrocytes and showed stable platelet enrichment (PRP/whole blood ratio 2.1 ± 0.3). Protein concentrations in LP-PRP did not differ across collection times. Despite marked interindividual variability, no time-dependent differences were observed in platelet or protein composition. These results demonstrate that LP-PRP is temporally stable, independent of blood sampling time. This robustness supports flexible clinical use and contributes to efforts toward PRP standardization in therapeutic practice.