463 CLINICAL RELEVRNCE OF THE INSULIN-LIKE GROWTH FACTORS

We have reviewed our experience with radioinmunoassays of the insulin-like growth factors, IGF-I and II, to determine their utility in the evaluation of short stature. IGF-I and II were treasured in normal (NL) (height 5-95%), normal short (NS) (height > 2 s.d. below mean, GH peak < 7ng/ml) and growth hormone deficient (GHD)children by radioimmunoassay using the NIADDK anti-serum for IGF-I and a specific antibody to the C-peptide region of IGF-II. An age-related boundary for IGF-I and a level of 300ng/ml for IGF-II were used to classify values as normal or low. Results are given in the table as [low values]/[total per group]. IGF-I is a far better indicator of GHD than IGF-II. Using a criterion of either low IGF-I or II, 62/65 (95%) of GHD cases and 18/195 (9%) of NL would have been identified. 5/7 false positives for IGF-I occurred below age 5 and 4/5 false negatives occurred above age 8. Interestingly, the proportion of low values for both IGF-I and II in the NS group are similar to those observed for the GHD group. We conclude that IGF-I and to a lesser extent IGF-II levels are useful in identifying a child with possible GHD. Our data also demonstrate significant overlap in IGF-I and II levels in GHD and NS children, suggesting that a subset of NS has abnormalities in physiologic GH secretion which are not revealed by provocative testing.