ISSN 1470-3947 (print)
ISSN 1479-6848 (online)

Searchable abstracts of presentations at key conferences in endocrinology

Published by BioScientifica
Endocrine Abstracts (2008) 15 P215 

How reliable is the short Synacthen test in assessing the integrity of the hypothalamo-pituitary-adrenal axis: comparison with the insulin tolerance test

Nimal Seneviratne, Niki Karavitaki, Vivien A Thornton-Jones & John A H Wass

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Background: Insulin-induced hypoglycaemia (ITT) is considered the gold standard method for the evaluation of the hypothalamo-pituitary-adrenal axis. The standard short Synacthen test (SST) has been proposed as an alternative, but it may be associated with falsely reassuring results and potentially serious sequelae.

Aim: To compare the serum cortisol response achieved in the SST with the one obtained during the ITT in patients with hypothalamo-pituitary disease and to investigate whether the former may obviate the need to perform the latter.

Patients and methods: The results from thirty patients (22 males, median age 39, range 17–63) who underwent both tests (ITT: 0.15–0.3 IU of soluble insulin/kg body weight, i.v. – SST:250 mcg Synacthen i.m.) were analysed retrospectively. In no subject the two tests were separated by any therapeutic intervention.

Results: Twelve patients had peak serum cortisol >580 nmol/l (time 30) in the SST and 17 had peak >580 nmol/l in the ITT. There was a positive correlation between peak serum cortisol in both tests (Spearman’s correlation coefficient=0.70, P<0.01). Among 12 subjects with peak >580 in the SST, 1 (8.3%) did not achieve peak >580 in the ITT. Among 18 with peak <580 in the SST, 6 (33.3%) achieved peak >580 in the ITT. These 6 subjects had median peak in SST of 541 (range 505–575). Among 17 with peak >580 in the ITT, 6 (35.3%) did not achieve peak >580 in the SST. Among 13 with peak in the ITT <580, 1 (7.7%) achieved peak >580 in the SST.

Conclusions: Using the cut-off of 580 nmol/l, the SST may overestimate cortisol deficiency, but the chance of missing this diagnosis is small. Cases with borderline peak serum cortisol in the SST require re-evaluation with an ITT; otherwise, and particularly when other pituitary hormone deficits are present, the SST suffices.

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