LAUSR

Dear Sir, Iron deficiency in blood donors is an important adverse consequence of frequent blood donations (Vuk et al., 2017). Numerous studies have been published so far with the aim of reducing this risk and improving the well-being of blood donors. Implementation of ferritin measurement is one of the most frequently proposed measures. However, despite revealing only manifest anaemia, for most blood collection facilities, determination of haemoglobin concentration is the only test measuring the donor iron status. Therefore, it is important to reduce possible interferences and other factors influencing the accuracy of the measurement results. Smokers have higher haemoglobin concentrations compared to non-smokers, and this effect is positively correlated with the number of cigarettes consumed (Whitehead et al., 1995; Milman & Pedersen, 2009). According to Milman & Pedersen (2009), the effect of smoking is greater in women. Increased haemoglobin concentration in smokers could be attributed to the increased carboxyhaemoglobin level. As the affinity of haemoglobin to carbon monoxide (CO) is much higher than for oxygen, the capacity of red blood cells to transport oxygen to the tissues will decrease. In addition, CO causes the shift of the haemoglobin dissociation curve to the left, reducing the ability of haemoglobin to deliver oxygen. When CO concentration is in sufficient quantity, it will result in tissue hypoxia and functional anaemia. As a result, erythropoietin production increases, resulting in secondary erythrocytosis (Nordenberg et al., 1990; CDC, 1998). We have investigated the effect of smoking on haemoglobin concentration in 1876 whole blood donors (1084 males and 792 females). The median age of male donors was 38·5 years, with interquartile range (IQR) 28·8–48·5 years, and of female donors was 39·8 years (IQR 28·8–51·4 years). Only blood donors eligible for blood donation were included in the study, which means that pulmonary diseases were not reported or discovered in the selection process. The measurement results were normally distributed according to the Smirnov–Kolmogorov test. In female donors, the mean haemoglobin concentration was 137± 8 g L−1 [95% confidence interval (CI)= 136·2–137·7] in non-smokers and 142± 9 g L−1 (95% CI= 140·6–143·0) in smokers (+3·6% on average in smokers). In male donors, the differences in haemoglobin concentrations between non-smokers