THE SHORT SYNACTHEN AND INSULIN STRESS TESTS IN THE ASSESSMENT OF THEHYPOTHALAMIC-PITUITARY-ADRENAL AXIS

OBJECTIVE The best dynamic test for the assessment of the hypothalamic -pituitary-adrenal axis and the interpretation of the cortisol levels, remain a matter of controversy. We aimed to establish normal ranges w ith current assays, for both the short Synacthen (SST) and insulin str ess tests (IST) and then to use these data to examine whether the SST can satisfactorily substitute for the IST in assessment of the hypotha lamic-pituitary-adrenal axis. DESIGN Thirty SSTs and 27 ISTs were perf ormed on different healthy volunteers. The results of all paired tests performed on patients in the last three years are reviewed. SETTING P rogrammed Investigation Unit. SUBJECTS Fifty-seven healthy volunteers and 166 patients. MAIN OUTCOME MEASURES Basal serum cortisol concentra tion and cortisol values obtained at 30 and 60 minutes during the SST compared to the maximum obtained with adequate hypoglycaemia (plasma g lucose < 2 mmol/l) during an IST. RESULTS From normal data the mean-2S D 30-minute value during the SST was 392 nmol/l and 60-minute value wa s 497 nmol/l. The maximal cortisol response (mean-SSD) during the IST was 519 nmol/l. Sixty patients failed the IST, none of whom had a basa l cortisol > 450 nmol/l and only six (10%) had a 30-minute cortisol va lue > 600 nmol/l. The 30-minute value provided a better index than the 60-minute value, The basal, 30 and 60-minute values during the SST al l correlated positively and significantly with the maximal cortisol on IST. The correlations persisted for all microadenomas and macroadenom as secreting prolactin, gonadotrophins or growth hormone, patients und ergoing either pre or post-adenomectomy evaluation, and in those patie nts who had received long-term steroids provided that the medication h ad been reduced and stopped two days prior to admission. CONCLUSIONS U sing a 30-minute cortisol value > 600 nmol/l as a cut-off, the short S ynacthen test provides a suitable substitute for the insulin stress te st, Adopting this policy will decrease the number of insulin stress te sts performed by one-quarter and thus provide a substantial saving wit hout detriment to patient care.