Endocrine Abstracts

JOINT326

Background: Insulin Tolerance Test (ITT) and Glucagon Stimulation Test (GST) constitute two most commonly used tests in assessment of anterior pituitary function in terms of both growth hormone (GH) and cortisol secretion. We compared concentrations of glucose, cortisol and GH during ITT and GST in 19 subjects (five males), mean age 33.8 years (range 19-60), mean BMI 27.8 kg/m² (range 16.5-47.6). Patients were investigated for amenorrhoea (n = 8), had history of pituitary macro- (n = 2), or microadenomas (n = 5), isolated diabetes insipidus (n = 1), iatrogenic glucocorticoid-induced adrenal suppression (n = 1), hypopituitarism after congenital CMV infection (n = 1), or history of cranial irradiation (astrocytoma), n = 1. Both Insulin Tolerance Test and standard fixed-dose GST (0, 30, 60, 90, 120, 150 and 180 minutes) were performed in all subjects.

Results: As expected, minimal glucose concentrations were lower during ITT (29.7±7.67 mg/dl, at 30 minutes of ITT) than during GST (73.6±9.67 mg/dl, at 180 minutes of GST, P < 0.001) though glucose fluctuations (ΔGlucose) were higher during GST (77.8±22.6 mg/dl vs 56.7±10.9 mg/dl, P = 0.002, for GST and ITT, respectively). There was, however, no difference in either cortisol (ΔCortisol 9.28±3.79 µg/dl vs 8.49±3.46 µg/dl, P = 0.4), or growth hormone fluctuations during both tests (ΔGH 10.23±10.36 ng/ml vs 10.52±9.67 ng/ml, P = 1.0, for GST and ITT, respectively).

Conclusion: Despite the absence of frank hypoglycaemia during GST, in contrast to ITT, both tests lead to similar increments in cortisol and growth hormone in adult individuals. Hence, Glucagon Stimulation Test should not be considered as an “inferior” option in comparison to Insulin Tolerance Test for assessment of an anterior pituitary function.