Evaluation of growth hormone secretion: provocative testing vs endogenous 24-hour growth hormone profile

A total of 55 children underwent hGH provocative testing with two or more provocative agents, and measurement of endogenous 24-hour hGH secretion. Patients were divided into groups according to their peak hGH secretory response to provocative testing and their mean 24-hour hGH concentration. Peak hGH response to provocative testing was significantly greater in control children and in children with hGH neurosecretory dysfunction (GHND) than in the classical hGH deficient group. Mean 24-hour hGH concentration was significantly greater in the control group than in either the classical hGH deficient or GHND groups. Responses to provocative stimuli were intermediate for the GHND group compared to the classical hGH deficient and the control groups. The mean peak hGH secretory response to insulin-induced hypoglycaemia in the GHND group was poor compared to controls and was greatest following clonidine. The mean peak hGH response to an intravenous bolus of growth hormone releasing hormone was intermediate for the GHND group compared to hGH deficient and control groups. Highest nocturnal peak, first hGH pulse after sleep, mean peak hGH pulse and total number of pulses were also intermediate for the GHND group compared to the other groups. The control group had significantly more pulses greater than 5 ng/ml than did the other groups. Night-time and daytime hGH pools were lower in the classical hGH deficient and GHND groups compared to controls; however, there was overlap between groups. Six of seven children in the GHND group have responded to exogenous hGH therapy with increased linear growth velocity. Measurements of endogenous 24-hour hGH secretion may identify a subgroup of hGH deficient children who are not detected by provocative testing yet who may respond to exogenous hGH therapy with improved linear growth.