A practical approach for complete blood count analysis following acute exercise: Capillary vs. venous blood sampling

Venipuncture is the standard technique for blood sample acquisition but requires expertise, larger volumes of blood, and can be challenging in special populations. Capillary sampling may provide an alternative, but its reliability is unclear for assessing hematological parameters, especially following acute exercise. The purpose of the study was to compare the agreement and accuracy of complete blood counts (CBC) from capillary and venous blood sampled before, immediately after a single bout of aerobic exercise, and into recovery. An exploratory purpose was to examine potential biological sex differences within the CBC between blood sampling sites. Recreationally active healthy adults (N=13 male and N=13 female) completed three visits including familiarization, graded exercise testing, and a 40-minute exercise bout at 90-98% of ventilatory threshold. Venous and capillary blood samples were collected simultaneously at rest, immediately post-exercise (0 h) and 30-minutes into recovery (0.5 h). White blood cells (WBC), lymphocytes (LYM), and neutrophils (NEUT) were strongly correlated at all timepoints (r>0.8, p<0.05) with low bias, and moderate level of agreement (LOA). Mixed cells (MXD), hemoglobin (HGB), and hematocrit (HCT) were strongly correlated at baseline (r>0.7, p<0.05), but showed weaker correlations following exercise. There were no differences in mobilization or egress of CBC outcomes between sites by sex except for lymphocyte egress. Males had lower lymphocyte egress in venous versus capillary sampling whereas females had higher lymphocyte egress in venous versus capillary sampling. These data indicate capillary sampling is an accurate alternative to venous sampling following acute exercise based on LOA and reliability data.