Assessment of growth hormone secretion in normal stature children using 24-hour integrated concentration of GH and pharmacological stimulation

The integrated concentration of serum GH (IC-GH) is used for the assessment of spontaneous GH secretion. In order to use the IC-GH as a diagnostic tool a normative reference range needs to be established. We determined the IC-GH by continuous blood withdrawal in 119 children of normal height, weight and growth rate. Although the mean IC-GH increased with pubertal status, 4.4 +/- 1.2 micrograms/L at Tanner I (n = 36), 5.5 +/- 2.1 micrograms/L at Tanner II-III (n = 43), and 5.8 +/- 1.6 at Tanner IV-V (n = 40) (P less than 0.03), there was a considerable overlap of individual IC-GH levels between the pubertal groups. Gender affected the mean IC-GH level slightly, but not the range. Although the mean IC-GH of girls tended to be higher than that of boys this difference was not statistically significant. Ninety five percent of the IC-GH values were above the 3.2 micrograms/L level. The response to pharmacological stimulation (clonidine, insulin, or arginine) was also evaluated in 68 of the subjects. The peak GH response to pharmacological stimulation (micrograms/L) with clonidine 21.0 +/- 10.7 (n = 66) was significantly higher than to either arginine 13.1 +/- 6.1 (n = 23) or insulin 14.2 +/- 6.3 (n = 19) (P less than 0.01). The peak response to clonidine increased significantly with pubertal status (P less than 0.001) and there was an interactive effect of gender and pubertal stage where the GH response of prepubertal boys exceeded that of prepubertal girls but the response of pubertal girls exceeded that of pubertal boys (P less than 0.02). The peak stimulated GH levels was correlated with IC-GH in this subgroup r = 0.52, P less than 0.0001). This study provides a large normative data base for IC-GH and the GH provocative tests in normally growing children of varying pubertal status.