Editor,—We were interested in the suggestion by Mølgaard and colleagues that whole body bone mineral content (BMC) measured by dual x ray absorptiometry (DXA) should be considered as a function of bone area.¹ Using the same type of DXA equipment (Hologic QDR-1000W) we measured whole body BMC in 300 normal girls aged 11–18 years.² Our results for whole body BMC, both as a function of bone area and age, were essentially identical to those of Mølgaard et al.¹ To assess the usefulness of area normalisation in patients we have analysed the results from 71 studies on 51 anorexic females aged 14–18 years. The patients’ clinical state was subdivided into “moderate” (n = 44) and “severe” anorexia (n = 27) based on a body mass index of 15.1–18.9 kg/m² and < 15.0 kg/m²respectively. Height was within the normal range for age and there was no significant difference in age or height between the two groups.

Z(Age) and Z(Area) were calculated using the predicted values and SDs for age matched and area matched normal subjects from Mølgaardet al.¹ Mean (SD) Z(Age) was −1.01(0.84) and −1.45 (0.95) for the moderate and severe anorexic groups respectively. For both groups Z(Age) was significantly lower than zero (p < 0.0001) as expected and the value for the severe anorexics was lower than that for the moderate anorexics (p = 0.05). However, Z(Area) was 1.85 (1.39) and 4.41(1.60) for the moderate and severe anorexic groups respectively. For both groups …