The pyridostigmine-growth-hormone-releasinghormone test in adults. the reference interval and a comparison with the insulin tolerance test

Abstract

The aim of this study was to evaluate the pyridostigmine-growth-hormone-releasing-hormone (PDGHRH) test for diagnosing GH deficiency (GHD) in adults. The participants fasted overnight. At 09.00 h, PD 120 mg was administered orally, this dose having been established in a dose-response study. Sixty minutes later, GHRH1 fig/kg body weight was administered intravenously. In 40 normal subjects, the peak GH responses were log-Gaussian distributed. The 2.5 percentile (-1.96 SD) of 42mU/l is used as the lower reference limit for a normal GH response to the PDGHRH test in adults. The PD-GHRH test was compared to the insulin tolerance test (ITT) in 47 patients with suspected GHD. We found consistent classification concerning normal and subnormal peak GH responses to the two tests in 44/47 patients using the conventional lower reference limit for a normal GH response to the ITT of 20 mil/I. Determination of IGF-I levels had limited value in diagnosing GHD in adults. The PD-GHRH test was compared to the GHRH test in 24 patients with suspected GHD. PD had a potentiating effect on the GHRH-stimulated GH response in 10/24 patients with normal GH responses to the PD-GHRH test, and a varying effect in 14/24 patients. There are no absolute contra-indications to the PD-GHRH test. We observed no severe side-effects. We conclude that the PD-GHRH test is safe, reliable and a potent stimulator of GH secretion in adults.