Urinary Cellular Responses to Extreme Endurance Exercise: Sex-Associated Patterns After a 150 km Ultramarathon

Extreme endurance exercise offers a field setting for characterizing urinary cellular responses across sexes. This prospective observational study examined paired baseline and immediate post-race urine from 16 women and 16 men completing a 150 km ultramarathon. Automated fluorescence flow-cytometric counts were assessed alongside physicochemical and reagent-strip outputs. Between-sex tests compared individual acute changes; post hoc Bonferroni adjustment retained the original eight-comparison family. Median erythrocyte changes were +1.70 cells/µL in women and +0.60 cells/µL in men, with a between-group distributional difference retained after adjustment (p = 0.032). Corresponding squamous-cell changes were +0.85 and +0.30 cells/µL; this nominal difference did not meet the adjusted threshold (p = 0.056). Leukocyte, bacterial, pH and specific-gravity changes showed no significant between-group contrast. Recorded protein, ketone and male-only 24 h observations provided descriptive context. The findings identify an endpoint-specific urinary phenotype, with the erythrocyte association providing the clearest statistical signal. They establish a focused empirical target for source-specific replication and mechanistic investigation; anatomical origin and clinical significance require additional assessment.