Variation in hemoglobin across the life cycle and between males and females.

WHO recommendations for hemoglobin (Hb) cutoffs to define anemia are based on a handful of studies conducted in the 1960s that did not include participants from all life stages. To evaluate whether there is a need to update Hb cutoffs, we conducted a narrative review of the literature to identify more recent studies that have reported Hb cutoffs in males and females in various life stages. We compiled information from 60 studies conducted around the globe between 1975 and 2018. Many studies reported cutoffs that were similar to WHO recommendations, but cutoffs identified in studies of infants, young children, premenopausal women, and the elderly tended to be lower than WHO recommendations, while cutoffs identified in studies of men tended to be higher than WHO cutoffs. Few studies excluded individuals with iron deficiency or inflammation, which limits the conclusions that can be drawn regarding normal reference ranges. Further research using more stringent exclusion criteria is needed to develop revised recommendations for Hb cutoffs to define anemia.