Differences between venous and capillary hemoglobin levels in men and women. (A) The mean difference and standard error between venous and capillary hemoglobin levels (ΔVC) in 35 985 paired capillary and venous samples were taken from 25 557 females and 10 428 males in whom the capillary hemoglobin was > 11.5 to < 12.5 g/dL and > 12.5 to < 13.5 g/dL, respectively, and from 81 male and 74 female first-time blood donors where the capillary hemoglobin levels were above the cutoff for inclusion in the original study group.¹  There is a significant change comparing lower capillary Hb with higher venous Hb (by Kruskal-Wallis, followed by Dunn posttest). The ΔVC increases in a linear manner as measured by Spearman correlation, in both females and males as the capillary hemoglobin levels in the groups decline (r = −0.9879, P < .0001 for the female group; r = −0.9152, P = .0005 for the male group). (B) The mean difference and standard error between venous and capillary hemoglobin levels (ΔVC) compared between age groups. The dot plot shows mean age versus mean ΔVC within each age group in men and women. Within the male cohort, there was a negative linear correlation; r = −0.978, P < .0001. ΔVC is lower in women and rises with increasing age. The linear correlation is much lower, and the slope is in the opposite direction; r = 0.7818, P = .0102. It is clear from the dot plot that ΔVC is stable in women until they reach their 50s, when there is a sizable increase. By the age of 65-69 years, ΔVC standard error in women overlaps with that of men.