Endocrine Abstracts

Introduction: Short Synacthen tests (SST) are expensive, inconvenient, time consuming and subject to Synacthen availability. Any strategy reducing the need for SSTs will improve its cost effectiveness and also improve patient satisfaction. In this regard indications for SST and assay specific pre-test cortisol levels (not all SSTs are done at 0900 h) may have clinical utility.

Methods: We retrospectively examined the indications for, time and place of testing, and the utility of pre-test cortisol concentrations of all SSTs done in the Aneurin Bevan University Health Board over a period of 12 months. Receiver-operating characteristic (ROC) curve analysis was undertaken for pre-test cortisol to obtain a cut off value for failure.

Results: We analysed 506 SSTs of which 106 (21%) were abnormal. SST failure was highest for the indications of “current therapy/weaning from steroids, and low random cortisol levels” (39.6%; P<0.001). There was no difference in outcome for indications such as hyponatraemia, postural hypotension and tiredness/fatigue. Median pre-test cortisol (interquartile range) were significantly different in those with abnormal SSTs compared to those with normal SSTs [147 (91–213) vs 298 (227–393), P<0.001]. There was a higher test failure rate in those who had an early morning SST compared to others (26.8 vs 19.5%, P = 0.001); but there was no difference when place of testing was compared (outpatient or inpatient). ROC curve analysis indicated SST failure with 100% sensitivity with pre-test cortisol of <47 nmol/l; and a normal SST with 100% specificity with cortisol >323 nmol/l.

Conclusions: This study indicates that (i) pre-test cortisol levels of <47 predicted SST failure with 100% sensitivity and cortisol of >323 predicted a normal SST with 100% specificity; (ii) in this group 141 tests may have been avoided if these cutoffs were applied with a significant cost saving; (iii) some indications had a higher predictability for SST failure, and those with lower predictability need supporting evidence before SST is undertaken.