The use of capillary blood for measurements of circulating ferritin.

The accuracy and reproducibility of using stored capillary blood for measurements of circulating ferritin were evaluated by comparison with simultaneous measurements on venous blood. In an initial study, the between- and within-sample variability of capillary determinations was about three times higher than with venous measurements, but the difference was reduced considerably by using capillary serum rather than plasma. With both serum and plasma, the mean ferritin in capillary specimens was 3 to 5% higher than in venous blood. These minor drawbacks with capillary measurements are outweighed by the benefit of improved compliance in prevalence surveys when finger-stick sampling can be used in place of venipuncture.