Background: The usefulness of IGF-I, IGFBP-3, and the urinary GH excretion in the diagnostic evaluation of growth retardation in boys with short stature was studied.
Subjects and method: Serum samples from two GH-stimulation tests and two 24-h urine samples were sent to a Central Laboratory to measure serum and urinary GH, serum IGF-I, IGFBP-3 and GHBP, both in absolute and standardized values (Z-score). Short children were classified as growth hormone deficient (GHD) (n = 25), and idiopathic short statured (ISS) (n = 54), on the basis of the peak stimulated GH concentration of < 7.5 microg/l or > or = 7.5 microg/l respectively. A group of 15 normally growing children and adolescents was also included.
Results: Height-velocity standard deviation score (HV)-SDS was lower and body mass index higher in GHD than ISS. Standardized IGF-I differed significantly by ANOVA among the three groups (p = 0.001). Multiple stepwise linear regression analysis with HV-SDS as dependent variable showed IGF-I SDS as the best predictor followed by peak GH clonidine response and uGH excretion. ROC curves showed optimum cut-off level for IGF-I SDS as 2.05 (sensitivity: 32%, specificity: 90%) and 1.14 for IGFBP-3 SDS sensitivity: 28%, specificity: 94%).
Conclusions: Standardized IGF-I and IGFBP-3 measurements were highly efficient only in diagnosis of severe GHD, but they show low sensitivity for the diagnosis of isolated idiopathic GHD as defined according to the low GH response to stimulation tests.