Assessment of somatotropic function in children with syndrome of biologically inactive growth hormone against a background of clonidine and insulin stimulation tests.

Abstract

Abstract. Background. Growth pathology caused by somatotropic insufficiency is one of the most urgent problems in pediatric endocrinology. An increase in the growth hormone (GH) level less than 10 ng/ml was traditionally considered a criterion for diagnosing somatotropic insufficiency in patients with short stature, when performing provocation tests. The purpose is to evaluate the effectiveness of clonidine and insulin provocation tests for the somatotropic hormone (STH) stimulation in diagnosing the syndrome of biologically inactive growth hormone (SBIGH). Materials and methods. A total of 158 patients with SBIGH (47 girls and 111 boys aged 8.30 ± 0.24 years) were examined. The study included patients with delayed growth more than 2 standard deviations. Basal and stimulated STH levels were determined using insulin and clonidine tests. A 4-day growth hormone sensitivity­ test was obligatorily performed for determining insulin-like growth factor 1 levels prior to the first GH injection and the day after the test completion. Results. The maximum increase in STH against a background of insulin and clonidine tests was above 10 ng/ml in all patients with SBIGH. Significantly higher maximum increase of STH parameters (p < 0.01) was noted in clonidine stimulation test than in insulin one. This was proved both in patients with SBIGH (17.79 ± 0.51 ng/ml and 13.83 ± 0.92 ng/ml, respectively) and in children of control group (16.81 ± 1.60 and 11.18 ± 0.70 ng/ml). Standard deviation score of insulin-like growth factor 1 was significantly lower (p < 0.001) in children with SBIGH than in control group. More pronounced changes were observed in prepubertal patients. Conclusions. Clonidine provocation test is more informative than insulin one, and causes a significantly higher stimulating maximum release of GH. It is recommended to start the investigation of STH function with clonidine test, which is safer for patients due to the absence of a risk of severe hypoglycemic conditions.