Plasma levels of insulin-like growth factor (IGF)-I, IGF-II and IGF-binding protein-3 in the evaluation of childhood growth hormone deficiency

Background: Traditionally, measurement of plasma IGF-I and more recently of IGFBP-3 are used to distinguish GHD from idiopathic short stature in slowly growing children, using a single blood sample. In earlier studies it was claimed that IGFBP-3 was superior to IGF-I, but more recently doubts around this claim have arisen. The role of serum IGF-II has never been studied extensively. On theoretical grounds, it can also be hypothesized that molar ratios of these peptides might be of additional value. Design: Retrospective, multicentre, cohort study. Patients: 96 children evaluated for short stature. Methods: Serum IGF-I, IGF-II, IGFBP-3 and various molar ratios were, after correction for age and sex using SD scores, compared to the maximum serum GH peak after two standard provocation tests using four different methods (t-test, chi(2), likelihood ratios and ROC curves). In addition, the correlations between these parameters and the short-term(1 year) and long-term (3 years) response to GH therapy were calculated. Results: IGF-I performed better than IGFBP-3, but the best results were achieved by the molar ratio IGF-I:IGF-II. However, IGFBP-3 correlated better with the short-term response to CH therapy than IGF-I or the ratios, and none of the parameters investigated was found to be related to the response of long-term GPI therapy.