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, χ², 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 GH therapy than IGF-I or the ratios, and none of the parameters investigated was found to be related to the response of long-term GH therapy.

Measurements of IGFBP-6 have been shown so far to be of relatively minor clinical relevance. The exceptions are chronic renal failure patients and subjects with large tumours and non-islet cell tumour induced hypoglycaemia who may exhibit elevated circulating levels of this IGFBP. The physiological significance of this observation remains to be elucidated. The possibility of quantifying IGFBP-6 by specific RIA will facilitate further in vitro and in vivo studies of its regulation and function in man.

Aim: This study was designed to investigate whether determination of plasma insulin-like growth factor (IGF)-binding protein-2 (IGFBP-2) levels could be of benefit in the evaluation of childhood growth hormone (GH) deficiency (GHD). Method: A retrospective analysis was performed on 91 prepubertal children referred for investigation of short stature. Maximal GH levels in plasma after provocative stimuli were between 1.0 and 93.0 mU/l, 6 subjects exhibiting peak values of <5 mU/l. Initially a GH peak of 20 mU/l was used as a cutoff limit to define GHD and idiopathic short stature (ISS) patients. The results of GH provocative tests were compared to age- and gender-based standard deviation scores (SDS) of plasma IGFBP-2, IGF-I, IGFBP-3 and the molar ratios of the latter two to IGFBP-2. The respective normative range values for these parameters were determined in plasma samples from 353 healthy children (i.e. 171 girls, 182 boys). Results: Circulating IGFBP-2 levels did not correlate with height SDS, height velocity SDS or the peak GH levels after provocative stimuli. A weak negative relationship was found between IGFBP-2 and IGF-I. Plasma levels of IGFBP-2 in GHD patients were higher than those of ISS children, who had normal levels. Although at the optimal cutoff point of –0.71 SDS 91.5% of the GHD patients were identified correctly, a substantial proportion (71.9%) of the ISS subjects also had IGFBP-2 levels above this limit. The use of various combinations of IGFBP-2, IGF-I, IGFBP-3 and the derived ratios only slightly improved the diagnostic efficiency as compared to the results of the individual tests. Neither IGFBP-2 nor the IGFBP-3/IGFBP-2 and IGF-I/IGFBP-2 ratios were found to be related to the short- (1 year) or long-term (3 years) growth response to GH therapy. Conclusion: It is concluded that none of the tests investigated, either alone or in various combinations, are reliable in either predicting the peak GH level after provocative stimuli in prepubertal short children or in predicting their growth response to GH.