Background: The insulin tolerance test (ITT), glucagon stimulation test (GST) and short Synacthen tests (SST) are employed in the evaluation of suspected cortisol and/or GH deficiency, with ITT considered the gold standard.1 We hypothesised that these dynamic tests may yield discordant results within individuals.
Methods: We performed a retrospective audit of adults who had undergone ITT plus either GST and/or 250mcg SST. Cortisol adequacy was locally defined as peak cortisol >550nmol/L at any time on ITT or GST, and at 30min on SST. GH adequacy was locally defined as peak GH >10mU/L at any time on ITT or GST. The primary outcome was discordance in cortisol and/or GH responses between the dynamic tests.
Results: Of 14 patients, 8 had ITT+GST and 7 had ITT+SST (including 1 patient who had all tests). Mean peak cortisols from ITT and GST in subjects who underwent both tests were 423 and 428nmol/L, respectively. In subjects who underwent ITT and SST, mean peak cortisols were 409 and 491nmol/L, respectively. Mean peak GH from ITT and GST in subjects with both results were 4.3 and 16.6mU/L, respectively. In total, 9 of the 14 patients had discordant results using the defined decision points. Of the 5 patients with cortisol discordance, 3 were cortisol-adequate on ITT and inadequate on GST or SST, whilst 2 were adequate on GST and inadequate on ITT. The 5 patients with GH discordance were all GH-adequate on GST and inadequate on ITT.
Conclusions: Cortisol and/or GH discordance was found in 64% of patients. Glucagon and Synacthen appeared more potent stimuli of hormone secretion than hypoglycaemia, consistent with recent data.2 However, 3 subjects showed cortisol adequacy on ITT and not on GST or SST suggesting inter- or intra-individual variability. We recommend centre-specific and test-specific decision points be considered in dynamic tests of suspected hypopituitarism.