Unreliability of classic provocative tests for the diagnosis of growth hormone deficiency

In this study we investigated 9 pre-pubertal children with blunted GH response to classic pharmacological stimuli in contrast with normal auxological evaluation. The children were followed to evaluate their growth velocity for a longer period before starting replacement GH therapy. To evaluate the pituitary reserve a supraphysiologic stimulus such as GHRH plus arginine was used. Serum GH levels were measured by a time-resolved immunofluorimetric assay before and after 1 μg/kg body weight iv injection of GHRH, while serum PRL, IGF-I, and insulin were evaluated only in basal conditions using an automatic immunometric assay. Out of 9 studied subjects, 7 underwent GHRH plus arginine administration and showed a normal GH response; the parents of the remaining 2 children refused the test. Normal serum levels of PRL, IGF-I, insulin, and a normal insulin sensitivity were observed in all children. After 1 yr, the growth rate in each patient was further improved and reached almost normal values. Our results further confirm that the decision to start replacement GH therapy should be based on both auxological parameters and laboratory findings. The GHRH plus arginine test appears to be useful to identify false GH deficiency in children showing a blunted GH response to classic stimuli in contrast with normal growth rate.