Capillary and venous haemoglobin levels in blood donors: a 42‐month study of 36 258 paired samples

Background EU law requires a haemoglobin of ≥ 12·5 g/dl for women or ≥ 13·5 g/dl for men at the time of donation. As capillary and venous haemoglobin values may differ in the same subject, we examined whether a capillary haemoglobin level of 12·0 g/dl for women or 13·0 g/dl for men, is equivalent to a venous haemoglobin level of ≥ 12·5 g/dl and ≥ 13·5 g/dl, respectively, to avoid unnecessary loss of blood donations. Methods Over a continuous 42‐month period, 36 258 paired capillary and venous samples were taken from 25 762 females and 10 496 males, when the capillary haemoglobin was < 12·5 g/dl and < 13·5 g/dl respectively. Results Venous haemoglobin levels were higher than capillary levels, with a mean difference of 1·07 g/dl (SD 0·68 g/dl), range ?2·2 to +3·25 g/dl for men (P < 0·001), and a mean difference of 0·67 g/dl (SD 0·65 g/dl), range ?2·5 to +5·4 g/dl for women (P < 0·001). The difference for the three consecutive winters was 0·78 g/dl (SD 0·081 g/dl) for females and 1·26 g/dl (SD 0·162 g/dl) for males and for the three consecutive summers was 0·56 g/dl (SD 0·089 g/dl) for females and 0·88 g/dl (SD 0·134 g/dl) for males: P < 0·001. Conclusions Capillary haemoglobin levels of 12·0–12·5 g/dl in healthy females or 13·0–13·5 g/dl in healthy males are substantively equivalent to venous haemoglobin levels of ≥ 12·5 and ≥ 13·5 g/dl for women and men respectively. This finding has permitted an additional 32 990 blood units to be collected over the period of the study, a gain of 9·4%.