Physiological predictors of hematological tier outcomes in canine platelet-rich plasma: a prospective observational...

Platelet-rich plasma (PRP) exhibits substantial inter-individual variability, yet the physiological factors influencing its composition remain poorly defined. Most studies evaluate PRP as a homogeneous product, potentially masking associations between donor-related characteristics and platelet parameters. This study aimed to determine how key physiological factors influence whole blood (WB) and PRP indices and to assess their relationship with platelet enrichment. Ninety-seven client-owned dogs were categorized according to sex, age, body condition score (BCS), fertility status, and activity level. PRP samples were stratified according to platelet enrichment (Q1 < 1.5×, Q2 1.5-2.5×, Q3 > 2.5×), which served as a descriptive framework for characterizing PRP heterogeneity. WB and PRP indices were analyzed using univariate methods and multivariable models, including linear regression to identify predictors of platelet enrichment and ordinal logistic regression as a complementary approach. Physiological factors were associated with variability in platelet morphological and compositional indices. Among the variables evaluated, BCS was the only physiological factor consistently associated with platelet enrichment across multivariable analyses. Higher BCS was associated with increased platelet enrichment and a higher probability of belonging to higher hematological enrichment tiers. Age was negatively associated with platelet enrichment in the multivariable linear regression model, but this association was not retained in the ordinal regression analysis. In contrast, sex, fertility status, and activity level showed no independent associations with platelet enrichment after adjustment for potential confounders. Correlation analyses revealed strong clustering among concentration-related indices [platelet count (PLT), plateletcrit (PCT), and large platelets (LARGEPLT)] and a consistent internal organization of platelet parameters within both WB and PRP. These findings indicate that platelet enrichment is primarily determined by preparation-related factors, whereas physiological factors contribute mainly to inter-individual variability in platelet structural characteristics. Among the physiological factors evaluated, BCS appeared to be the most relevant source of biological variability in platelet enrichment. Platelet enrichment and platelet structural phenotype therefore represent related but distinct dimensions of PRP characterization. Future studies incorporating functional and biochemical markers are needed to determine the biological significance of the structural variability described here.