Comparison of the diagnostic utility of the simplified and standard i.m. glucagon stimulation test (IMGST).

OBJECTIVE: To compare the peak GH and cortisol responses to the simplified and standard i.m. glucagon stimulation test (IMGST) in order to determine whether the use of a simplified form of this test results in a loss of diagnostic utility. PATIENT AND
DESIGN: A retrospective study of 35 consecutive patients with pituitary disease who underwent a standard IMGST to measure GH (n = 34) or cortisol (n = 21) reserve at the programmed investigation unit of the Northern General Hospital, Sheffield. MEASUREMENTS: Cortisol, glucose and GH levels were measured at baseline and 30, 60, 90, 120, 150, 180, 210 and 240 min during the standard IMGST. We used the hormone levels at baseline, 150 and 180 min for the simplified IMGST and compared the cortisol and GH responses achieved.
RESULTS: The median (range) peak GH and cortisol responses to simplified and standard IMGST were comparable 4.2 (0.5-47.5) vs 5.4 (0.5-47.5) mU/l (P = 0.75) and 635 (306-1669) vs 647 (306-1669) nmol/l (P = 0.801), respectively. Using the standard 'cut-off' points to assess GH (9 mU/l) or cortisol deficiency (580 nmol/l) there was no significant loss of diagnostic utility (P = 0.98 and P = 1.00, respectively).
CONCLUSIONS: The simplified and standard IMGST have a similar diagnostic utility. The simplified IMGST could replace the standard IMGST as a screening test for GH and cortisol reserve in pituitary disease. The insulin-induced hypoglycaemia stress test can be reserved for cases in which a second assessment of pituitary reserve is clinically indicated or because of an indeterminate biochemical result.