How (not) to diagnose growth hormone deficiency in adults: stimulated serum concentrations of growth hormone in healthy subjects and in patients with pituitary macroadenomas.

The secretion of growth hormone (GH) stimulated by GH-releasing hormone ([GHRH] 100 micrograms intravenously [IV]) was determined in 33 patients with nonfunctioning pituitary macroadenomas before and after transsphenoidal adenomectomy and in 28 controls. Patients who needed substitution therapy for at least one additional pituitary hormone presented with lower GH secretion than the remaining patients with pituitary tumors. However, there was a marked overlap of stimulated GH secretion between these two groups (3.2 +/- 4.3 ng/mL and 7.2 +/- 6.6 ng/mL, respectively) and between either group with the control group (7.1 +/- 5.5 ng/mL). In an independent investigation, the effect of IV GHRH (100 micrograms) on the secretion of GH in seven healthy volunteers was shown to be comparable to that seen during an insulin tolerance test ([ITT] 0.1 U/kg IV). Thus, the GHRH stimulation test, a simple and comparatively unharmful procedure, is a useful alternative to the ITT in patients with potential pituitary defects. However, the pronounced overlap of stimulated serum GH concentrations in patients with pituitary macroadenomas and those estimated in healthy subjects and in patients with nonpituitary diseases underlines the difficulty in biochemically defining acquired GH deficiency in adults. We suggest that GH therapy in adults should primarily be instituted in patients with additional defects in anterior pituitary function.