Distribution of serum insulin-like growth factor 1 (IGF-1) concentrations in 35 normal (°) and 23 hypopituitary (•) subjects. There is an overlap of serum IGF-1 concentration between the two groups with 70% (16 of 23) of hypopituitary individuals having concentrations within the range of normal subjects. (Adapted with permission, from Hoffman DM, O’Sullivan AJ, Baxter RC, Ho KKY. Diagnosis of growth-hormone deficiency in adults. Lancet 1994; 343: 1065–8).