Capillary Blood Sampling for Assessing Metabolic Profiles of PBMCs: Comparisons with Venepuncture at Rest and Post-Maximal Exercise

Peripheral blood mononuclear cell (PBMC) bioenergetic profiling has emerged as a promising minimally invasive tool for assessing immunometabolic health, yet traditional venepuncture presents practical barriers for certain populations and longitudinal studies. This study examined PBMC bioenergetic profiles from upper-arm capillary blood using the Tasso+ device and compared these to traditional venepuncture. Healthy adults provided paired capillary and venous blood samples at rest and following maximal exercise. PBMCs were isolated and assessed using Seahorse XF technology for mitochondrial respiration and glycolytic function, alongside haematological and T-cell immunophenotyping via flow cytometry. Bland–Altman analysis demonstrated narrow limits of agreement and small mean bias between sampling methods for T-cell subsets and normalised bioenergetic parameters, whereas absolute bioenergetic rates showed wider limits of agreement with a consistently greater negative bias, indicating systematically lower values in capillary compared with venous samples. Formal equivalence testing confirmed method equivalence for only total CD4+ T cells and CD4+ naïve T cells at rest. For bioenergetic parameters, equivalence was demonstrated for proton leak respiration, mitochondrial health index, ATP supply rate, and glycolytic metrics. Absolute mitochondrial and glycolytic rates were not equivalent between methods. Both sampling methods preserved PBMC activation capacity following PMA/ionomycin stimulation. Our findings support capillary blood sampling using the Tasso+ device as a minimally invasive alternative to venepuncture for PBMC metabolic phenotyping and immunological assessments. However, caution should be exercised if using the methods interchangeably, given that only selected bioenergetic parameters and T-cell subsets demonstrate acceptable equivalence.