The insulin-like growth factor-I (IGF-I) generation test as an indicator of growth hormone status

OBJECTIVE: The aim of the study was to evaluate the IGF-I generation test (IGF-I gen) as a possible indirect test of Growth Hormone (GH) secretory status. METHODS: Sixty-five GH deficient (GHD 1 and 2) and 86 control children were studied. Children in the GHD-1 subgroup (n=33) had low GH values (<10 mu g/L) after clonidine and levo-dopa while those in the GHD2 subgroup (n=32) had normal GH values after pharmacologic provocation but low 24-hour GH secretory rates compared to 187 Normal Statured (NS) children. Of the 86 controls, who underwent IGF-I gen, 50 were NS and 36 Short-Statured (SS). Serum IGF-I was measured prior to and daily during hGH administration (hGH 0.033 mg/kg/day x 4 days). RESULTS: The prepubertal and pubertal GHD-1 and GHD-2 children had low baseline IGF-I values but their peak IGF-I values during the IGF-I gen reached those of the controls. The percent increase of IGF-I during the test was greater in the GHD groups than in the controls; in the prepubertal groups: 516 +/- 58% in the GHD-1, 433 +/- 50% in the GHD-2, 106 +/- 12% in the NS, and 102 +/- 18% in the SS (p=0.001); in the pubertal groups: 191 +/- 28% in the GHD-1, 141 +/- 20% in the GHD-2, 48 +/- 8% in the NS, and 61 +/- 17% in the SS (p=0.003). CONCLUSIONS: The IGF-I response during the IGF-I gen seems to reflect the GH status in children.