1. An epidemiological study of iron status in general practice has been undertaken. An age-sex register was established and a 10% stratified random sample (194 males and 220 females) of the patients above the age of 15 years was studied. A full blood count, serum Fe concentration, transferrin saturation and serum ferritin concentration were measured and correlated with clinical features associated with Fe deficiency.
2. The geometric mean for serum ferritin for males was 77 μg/1 (20–196 μg/1) and for females 37 μg/1 (8–177 μg/1). A low serum ferritin (male < 30 μg/1, female < 20 μg/1) in the absence of anaemia was found in fifteen males and thirty-five females. In this group forty patients had clinical features which are aetiologically associated with Fe deficiency. The incidence of similar features in a control group of thirty-three patients was seven.
3. It is suggested that this is indirect evidence that serum ferritin concentration is the most sensitive monitor of Fe status enabling the detection of pre-anaemic Fe deficiency.