Serum levels of insulin-like growth factor I in 152 patients with growth hormone deficiency, aged 19-82 years, in relation to those in healthy subjects

Serum insulin-like growth factor I (IGF-I) levels within normal range for a ge have been reported to be common in adults with GH deficiency (GHD). Ther efore, serum IGF-I levels were determined in 152 consecutive patients (71 w omen and 81 men) with evidence of hypothalamic-pituitary disorders or previ ous cranial radiation, who fulfilled the presently used criteria for GHD i. e. peak GH response below 3 mu g/L at stimulation test. Patients treated fo r acromegaly were excluded. Forty-three patients, aged 19-63 yr, had childh ood onset GHD, and 109, aged 23-82 yr, had adult-onset GHD. Their IGF-I lev els were expressed in SD scores in relation to normal reference values base d on 448 healthy subjects, aged 20-96 yr (247 women and 201 men). In health y subjects a linear inverse correlation, without gender difference, was fou nd between logarithmic transformed IGF-I levels and age (r = -0.774; P < 0. 001). In contrast, no age dependency was found in GHD patients. All patient s with childhood-onset GHD had IGF-I values below -2 SD, significantly lowe r than those in adult-onset GHD patients (-6.2 +/- 0.3 vs. -3.2 +/- 0.2 SD score; P < 0.001). In patients with adult-onset GHD, 34% of the IGF-I level s were within normal range, increasing to 40% in the subgroup above 60 yr o f age, in whom 86% were diagnosed with hypothalamic-pituitary tumors. Norma l IGF-I was more common in men than in women, but no difference was observe d between patients with panhypopituitarism and those with partial pituitary insufficiency. High frequencies of IGF-I levels within the normal range we re found in GHD patients with pituitary tumors (20 of 57 nonsecreting pitui tary adenomas, 5 of 15 prolactinomas, 6 of 12 Cushing's disease, and 4 of 2 5 craniopharyngiomas), but in only 2 of 43 patients with GHD due to other c auses. In conclusion, an IGF-I level below -2 SD seems to be of diagnostic value i n GHD with onset in childhood or early adulthood, whereas values within nor mal range are common in patients over 60 yr of age, especially those with p ituitary tumors. The outcome of GH replace ment therapy may reveal whether the addition of IGF-I as a diagnostic criterion is of predictive value in o lder patients.