Growth hormone response to oral clonidine test in normal and short children

Abstract

We evaluated the growth hormone (GH) response to an acute Clonidine test (0.15 mg/m² po) in 30 normal prepubertal children (stature between the 3rd and 97th centile), in 29 short children (stature <3rd centile for age) with height velocity (HV) >10th centile and in 20 short children with HV <10th centile. The three groups had comparable chronological ages. After clonidine administration mean peak GH levels were similar in the three groups (19.4±9.8, 17.7±8.8 and 14.6±8.9 μg/l, mean±SD, respectively). By chosing 10 μg/l as the limit for a normal response we found that stimulated GH levels had a sensitivity of 50% and a specificity of 83% in identifying children with suspected GHD (short children with subnormal HV). The diagnostic accuracy was almost superimposable, for cutoff values of 10 and 12 μg/l. Eight of the 10 children with subnormal HV and a GH peak <10 μg/l had a GH peak <10 μg/l also after a second stimulation test. Six of the 29 short children with normal HV had a GH peak <10 μg/l. Only one of them had a GH peak <10 μg/l after a second stimulation test. Five of the normal children had peak GH levels <10 μg/l. These results indicate that HV is a useful variable to predict the GH response to an acute GH stimulus, since the great majority of children with a normal growth rate had a normal GH response to at least one stimulation test.