Measurement of serum free IGF-I in diagnosis of growth hormone deficiency

Abstract

Serum levels of total insulin-like growth factor-I (IGF-I) are growth hormone (GH) dependent and can be used as the screening tool for GH deficient status. However, most of them are bound to IGF-binding proteins, leaving less than 1 per cent in the free or unbound forms which represent the active biological fractions. Serum free IGF-I levels were measured by radioimmunoassay (IRMA) in 48 short children with various conditions. We found that the means ± SEM of free IGF-I in children with panhypopituitarism (PAN) and complete growth hormone deficiencies (cGHD) were significantly lower than those in sex and age matched normal children (0.02 ± 0.01 vs 2.01 ± 0.7 ng/ml, p = 0.0006 and 0.42 ± 0.18 vs 1.72 ± 0.27 ng/ml, p = 0.0007 respectively) but not in children with partial growth hormone deficiencies (pGHD) (0.91 ± 0.3 vs 1.97 ± 0.4 ng/ml, p = 0.27) and idiopathic short stature (ISS) (0.94 ± 0.3 vs 1.95 ± 0.6 ng/ml, p = 0.13). However, when we classified the pGHD children into 2 groups according to IGFBP-3 SDS for normal Thai children, we found that the mean of free IGF-I levels in pGHD children with IGFBP-3 SDS ≤ -1.3 was significantly lower than that of the controls. (0.68 ± 0.55 vs 2.66 ± 0.71 ng/ml, p = 0.04) In conclusion, the measurement of free IGF-I level can be used to evaluate the GH status of short children and might be used as a guide when starting treatment.