Endocrine Abstracts

The use of the simplified IM glucagon stimulation test (IMGST) over its standard counterpart in the diagnosis of GH and cortisol deficiency has been advocated. Despite apparent comparable diagnostic utility, the simplified IMGST is capable of producing false positive results, raising the potential for misdiagnosis if relied upon exclusively.

The aim of this study was to re-evaluate the diagnostic utility of the two forms of the IMGST, ascertaining the magnitude of any discrepancy.

One hundred and thirty three IMGSTs performed at our centres were analysed retrospectively. Following 1 mg IM glucagon, GH and cortisol levels were measured at 0, 30, 60, 90, 120, 150 and 180 min during the standard IMGST. Values at 0, 150 and 180 min were used for the simplified test. A GH level≥9 mU/l and cortisol≥500 nmol/l was accepted as representative of hormone sufficiency.

Sixty-three tests (47.4%) were performed on males, 70 (52.6%) on females. Median age at testing was 44.8 (interquartile range (IQR) 30.6–58.9) years. Using the standard IMGST, 73 tests achieved a GH level≥9 mU/l. GH peak occurred at 0, 30, 60, 90, 120, 150 and 180 min in 6.8%, 4.1%, 1.4%, 5.5%, 16.4%, 46.6% and 19.2% of these tests respectively. Nine of these 73 tests (12.3%) failed to achieve the GH threshold using the simplified IMGST. No differences were observed in patient age or sex between groups (P>0.05). A trend was observed between radiotherapy exposure and false positive results using the simplified IMGST (P=0.11). Twenty-three patients achieved a cortisol level≥500 nmol/l with no discrepancies observed between the tests.

This study demonstrated a significant false positive rate (12.3%) when using the simplified IMGST in the diagnosis of adult GHD. In patients for whom additional tests are contraindicated, use of the simplified form may result in incorrect diagnosis and initiation of inappropriate, expensive treatment.