Can a glucagon stimulation test characterized by lower GH cut-off value be used for the diagnosis of growth hormone deficiency in adults?

Abstract

The aim of this study was to assess diagnostic values of insulin tolerance test (ITT), glucagon stimulation test (GST), and insulin like growth factor-I (IGF-I) level, to find optimal GH cut-off values for GST, and to evaluate efficiencies of patient age, gender, body-mass index (BMI), and additional pituitary hormone deficiencies (PHDs) in the diagnosis of growth hormone deficiency (GHD). This retrospective study involved 216 patients with a pituitary disease and 26 healthy controls. Age, gender, BMI, medical histories, and hormonal data including baseline and stimulated hormone values were evaluated. Three cut-off values for peak GH responses to stimulation tests were evaluated: (a) 3.00µg/L on ITT, (b) 3.00µg/L on GST, and (c) 1.07µg/L on GST. According to the ITT, GST with 3.00µg/L cut-off, and GST with 1.07µg/L cut-off, GHD was present in 86.1, 74.5, and 54.2% patients, respectively. Patient age, BMI, and number of PHDs, but not gender, were found to be correlated with IGF-I and peak GH concentrations. All patients with an IGF-I concentration ≤95ng/ml or ≥3 PHD had GHD. None of the patients with adequate GH response to the GST with 1.07µg/L cut-off, but blunted responses to ITT and GST with 3.00µg/L cut-off, had ≥3 PHDs. 12 out of 26 (46.2%) healthy subjects failed the GST with 3.00µg/L cut-off, but not with 1.07µg/L cut-off. Patient age, IGF-I, BMI, and number of PHDs are efficient factors associated with the diagnosis of GHD. A 4h GST with a diagnostic GH threshold of 1.07µg/L seems to be a good diagnostic method for GHD.