Population study of ctHb: challenging WHO definition of anemia

Anemia is the collection of signs and symptoms of reduced oxygen delivery to tissues as a result of a reduction in the number of red cells and/or reduction in blood concentration of hemoglobin. In clinical practice, anemia is diagnosed if the blood concentration of hemoglobin (ctHb) is abnormally low. 

The World Health Organization (WHO) has defined anemia as ctHb < 130 g/L for men and < 120 g/L for women. The validity of this definition is examined in one of the largest population studies of ctHb ever conducted. The entire adult population of the town of Tromso in Norway were invited. In total 26,530 (75 % of population aged >24 yrs) had their ctHb measured. 

From this massive database a ctHb reference range (2.5-97.5 percentile) was constructed. For all men this was 129-166 g/L and for all women 114–152 g/L. Using this reference range, then anemia is defined as ctHb < 129 g/L for men and < 114 g/L for women. 

When the WHO criteria were applied to this population, the prevalence of anemia in men was not significantly different from that which would be obtained if the reference range was used to identify anemia. However, the prevalence of anemia among women was found to be 2-3 times higher if the WHO criteria are used rather than the constructed reference range. 

The authors conclude that application of WHO criteria might result in the medicalization of healthy women. The database provides confirmatory evidence of the gradual decline in mean ctHb with age in men and the premenopausal increase and postmenopausal decrease of mean ctHb among women. Obesity and cigarette smoking were both found to increase ctHb.