Background. Red blood cell (RBC) transfusions are given as "number of units" without considering the haemoglobin (Hb) content of these units. Donor factors influencing Hb level in whole blood donors and, ultimately, in RBC units have not been studied.
Materials and methods. Donor data for a period of 1.5 years were retrospectively analysed and the effects of age, gender and weight on the Hb level of the donors were determined. The correlation between donor's Hb concentration with total Hb in the RBC unit was analysed. Additionally, actual Hb content of 125 RBC units was determined. The total Hb content of these RBC units was also mathematically calculated based on the blood donors' Hb. The ability of this mathematically calculated Hb to predict actual Hb content per RBC unit was then analysed.
Results. The mean Hb level in female donors was 1.79 g/dL lower than in the male donors (p<0.001). Increasing age was associated with a lower mean Hb in the donors (p<0.01), while a higher body weight correlated weakly (r=0.06) but significantly with increased mean Hb (p<0.01). Logistic regression analysis showed that in blood donors, female gender had a stronger influence on lowering the mean Hb than either older age or lower weight. A variation of nearly 100% (42.3-80.8 g Hb per unit) was seen in the total Hb content of the RBC units tested. Mathematically calculated Hb content correlated well (r=0.6; p<0.01) with the actual Hb content of the RBC units.
Discussion. We demonstrated the effect of gender, age and weight on Hb levels in whole blood donors. Dissimilarities in the donor Hb caused nearly 100% variations in the Hb content of the RBC units. It would, therefore, be prudent to label RBC units with their total Hb content. This total Hb content can be predicted fairly accurately from the donor's pre-donation Hb level.
Keywords: pre-donation Hb, blood transfusion, Hb increase, RBC overtransfusion, Hb content.