Pre-test Cortisol Levels in Predicting Short Synacthen Test Outcome: A Retrospective Analysis

Abstract

Objective: Short Synacthen tests (SSTs) are expensive, dependent on Synacthen availability, and need supervision. To reduce SST testing, we examined the utility of pre-test cortisol (Cort0) and related parameters in predicting outcome. Design and Measurements: We retrospectively examined the following in all SSTs; (i) Cort0 (ii) indications (iii) and time and place of testing. Receiver operated characteristic (ROC) curves were devised for Cort0 to obtain the best cut-off for outcome prediction in those who had SSTs between 8 and 10 am (Group 1) and at other times (Group 2). Results: Of 506 SSTs, 13 were unsuitable for analysis. 111/493 SSTs (22.5%) were abnormal. (1) ROC curves predicted – (a) SST failure with 100% specificity when Cort0 was ⩽124 nmol/L (Group 1), or ⩽47 (Group 2); (b) a normal SST with 100% sensitivity when Cort0 ⩾314 nmol/L (Group 1) and ⩾323 nmol/L (Group 2). (2) There was significant correlation between Cort0 and 30-minute cortisol ( rs = 0.65-0.78, P < .001). (3) Median Cort0 was lower in those who failed SSTs compared to those who passed (147 vs 298 nmol/L respectively, P < .001). (4) SST failure was commoner in Group 1 vs 2 ( P = .001). (5) There was no difference in outcome between out-patient and inpatient SSTs. (6) SST failure was most common for ‘steroid related’ indications (39.6%, P < .001). Conclusions: This study indicates that (1) Cort0 ⩾ 323 (Group1) and ⩾314 nmol/L (Group 2) predicted a normal SST with 100% sensitivity; (2) Using these cut offs 141/493 (28.6%) tests may have been avoided; (3) supporting evidence should be considered in those with a lower pre-test predictability of failure.

European Society of Endocrinology and Endocrine Society Joint Clinical Guideline: Diagnosis and Therapy of Glucocorticoid-induced Adrenal Insufficiency

“…The interpretation of serum cortisol varies depending on the assays used. Available techniques for measuring serum cortisol listed from least to most accurate methods are immunoassays using polyclonal antibodies, immunoassays using more specific monoclonal antibody to cortisol, and liquid chromatography-tandem mass spectrometry ( 57 , 94 , 95 ). For example, in a large study of patients undergoing 250 µg ACTH (1-24)-test, baseline cortisol that excluded adrenal insufficiency varied between 336 (12.2 μg/dL) and 506 nmol/L (18.3 μg/dL) when measured by three different immunoassays ( 57 ).…”

ACTH Stimulation Test for the Diagnosis of Secondary Adrenal Insufficiency: Light and Shadow

“…As discussed in the following paragraph, the interpretation of cortisol value, both at the baseline and stimulated, depends on the assay used for the measurement. According to the results of this study, if the cortisol evaluation is made with immunoassays using monoclonal antibodies, the grey range of 2016 guidelines potentially tighten even more allowing to identify of a narrower population to test [ 13 ]. In this context, the most recent studies stressed the importance of selecting patients to test according to the pretest probability of SAI that should be quantified by evaluating the patients’ clinical background and the morning cortisol levels [ 14 , 15 ].…”