Capillary Blood as a Potential New Matrix for the Athlete Biological Passport: A Field-Based Comparison Study

The hematological module of the Athlete Biological Passport (ABP) is based on venous blood sampling, which is invasive and operationally demanding. Liquid capillary blood sampling can offer a less invasive alternative, but data from routine anti-doping field collections remains limited.

This study aimed to evaluate the suitability of liquid capillary blood collected using Tasso+ EDTA devices as an alternative matrix to venous blood for the hematological module of the ABP in routine anti-doping controls.

A total of 209 paired venous and capillary blood samples were collected from athletes across thirteen different sports disciplines during out-of-competition controls in Spain. Both types of samples were analyzed using the same ISO/IEC 17025-accredited hematology method (Sysmex XN). Analytical concordance for key ABP parameters was statistically assessed, athlete perception was evaluated by a questionnaire, and the impact of capillary-derived values on real longitudinal ABP profiles was also explored.

Athlete acceptance of capillary blood collection was high, with minimal pain reported. A total of 44 samples were excluded due to pre-analytical problems, mainly coagulation of the capillary blood sample. Regarding the comparison of results, a strong agreement was observed for primary and secondary ABP markers, with correlation coefficients ≥ 0.9 for hemoglobin, reticulocytes, OFF-score and ABPS. Biases between matrices were small and mostly within acceptable limits, whereas platelet count was the only parameter with poor concordance. Most capillary values did not affect the longitudinal ABP interpretation.

Liquid capillary blood is a valid alternative to venous blood for most hematological parameters of the ABP, supporting its potential use in routine anti-doping testing, while acknowledging pre-analytical limitations.