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

EU law requires a haemoglobin of > or = 12.5 g/dl for women or > 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 > or = 12.5 g/dl and > or = 13.5 g/dl, respectively, to avoid unnecessary loss of blood donations.

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.

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.

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 > or = 12.5 and > or = 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%.