USEFULNESS OF IGF-I ASSAY FOR THE DIAGNOSIS OF GH DEFICIENCY IN ADULTS

IGF-I is the best marker of GH secretory status but it also depends on the nutritional status and peripheral hormones such as insulin, gluco corticoids, thyroid hormones and gonadal steroids. Though monitoring I GF-I levels is:he best way for evaluating appropriate GH replacement, the usefulness of IGF-I assay in the diagnosis of adult GM deficiency (GHD) is still matter of debate. To clarify this point in a large popu lation of GHD adults (no.=135, 64 women and 74 men; age, mean+/-SE: 43 .8+/-1.4 yp, range 20-80 yr) we studied IGF-I levels, their reproducib ility and association to peak GH response to GHRH+arginine (GHRH+ARG) test and insulin tolerance test (ITT). The results in GHD were compare d with those in a large population of normal subjects (no.=336, 233 wo men and 103 men, aged 20-80 yr). Mean IGF-I levels in GHD (77.8+/-4.9 yg/l) were clearly lower (p<0.001) than those in normal subjects (170. 2+/-4.7 yg/l). In Childhood Onset GHD (CO-GHD; no.=40; lage, mean+/-SE : 27.8+/-1.5 yr) IGF-I levels were lower than those in Adult Onset GHD (AO-GHD; no.=95, age, mean+/-SE: 50.7+/-1.4 yr) (56.6+/-9.7 vs 87.1+/ -5.4 mu g/l, p<0.0003). In both GHD and normal subjects IGF-I levels s howed good, reproducibility (r=0.92, p<0.00001 and r=0.62, p<0.00001, respectively). in GHD, but not in normal subjects, IGF-I levels were p ositively associated to peak GH responses to GHRH+ARG (r=0.57, p<0.000 01); on the other hand, the GH peak after ITT was not associated to IG F-I in GHD, In normal subjects, but not in CHD, IGF-I levels were nega tively associated to age (r=-0.60, p<0.00001). Considering individual IGF-I levels there was a clear overlap between GHD and normal subjects . However, this overlap was strongly dependent on age. In fact, in the third and fourth decade of life 83.6% of GHD had IGF-I severs below t he 3rd centile of normal values; on the other hand, in the fifth-sixth decade and in ageing 47% and only 12% of GHD, respectively, had IGF-I levels low for age. In conclusion, our results demonstrate that IGF-I levels represent a reproducible marker of GH status and are reduced m ore in CO-GHD than in AO-GHD adults. An overlap exists between GHD and normal subjects, however this is small up to the 4th decade of life. Thus, though normal IGF-I levels do not rule-out the existence of GHD, up to 40 yr low IGF-I levels strongly point to GHD if malnutrition an d liver disease have been ruled out. (J. Endocrinol. Invest. 21: 506-5 11, 1998) (C) 1998, Editrice Kurtis.