Aim-To identify the optimum age to screen for iron deficiency, the normal distribution of haemoglobin and ferritin in a representative population sample was investigated. Methods-Normal values for haemoglobin and ferritin were measured from heel prick capillary samples obtained from a representative cohort of 1175 infants at 8 months old who were randomly selected from children taking part in the Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC). Results-Haemoglobin was normally distributed: mean (SD) 117 (11) g/l, 95% confidence interval (CI) 116 to 118, and range 72-153 g/l. Ferritin was log normally distributed: geometric mean 38.5 mu g/l, 95% CI 37.0 to 39.9, range 7.1-224 mu g/l. The 5th centile for haemoglobin was 97 g/l and for ferritin 16.9 mu g/l. No correlation was found between haemoglobin and ferritin. Multiple regression analysis showed ferritin concentrations to be positively related to birth weight (P<0.0001) and the sex of the child (girls with higher concentrations) (p<0.0001) but negatively with the child's weight at 8 months (p<0.0001). Haemoglobin concentrations were positively related to the child's weight at 8 months (p=0.04). Neither haemoglobin nor ferritin concentrations were related to social class as measured by maternal education level. Conclusion-These data define the normal range for haemoglobin and ferritin in capillary samples in the UK population, and suggest that anaemia is common in infancy. Using current recommendations, 23% of infants would be identified as anaemic. For British infants at 8 months of age, a more representative 'cut off for anaemia would be haemoglobin concentration <97 g/l and for iron deficiency ferritin <16 mu g/l.
