Either Abstract

(Adults - Adrenal), #220531638388

Value Of 30 and 60-Minute Cortisol Value During Short Synacthen Test – Can We Do Away With One Or The Other?

Khoo Jun Kit, 1Endocrine Unit, Department of Medicine, University Malaya, Kuala Lumpur, Malaysia; Pavai Sthaneswar, Chemical Pathology Unit, Department of Pathology, University Malaya, Kuala Lumpur, Malaysia; Shubash Shander Ganapathy, Institute for Public Health, National Institutes of Health, Ministry of Health Malaysia; Jeyakantha Ratnasingam, 1Endocrine Unit, Department of Medicine, University Malaya, Kuala Lumpur, Malaysia

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Introduction

The short synacthen test (SST) using 250mcg synthetic ACTH is the most widely used test to identify adrenal insufficiency (AI). The standard testing requiring both 30 and 60-minute cortisol values adds to resource utilisation and additional cost. We examine the utility of 30-minute versus 60-minute single time point cortisol values in identifying AI, compared against the convention of values at both time points.

Methods

Retrospective analysis of SST done at a single centre between 2018-2021. Serum cortisol was measured at 0, 30 and 60 minutes after 250mcg of intravenous synacthen. Adequate response was defined as cortisol value of ≥500nmol/L at either or both time points. We compared 30 and 60-minute values against overall response during SST.

Results

A total of 360 patients (age: 61.5±17.7years, 44% male) were studied. Indications for SST were: exogenous steroids use (41%), pituitary disease (13%), low morning cortisol (27%), hyponatremia (6%), hypotension (4%) and others (9%). Median (IQR) of cortisol values at 0, 30 and 60 minutes were 250 (165-371), 581 (427-724), and 651 (479-819) nmol/L respectively. 217 (60.3%) had adequate response and 96 (26.7%) had inadequate response at both 30 and 60 minutes respectively. 42 (11.6%) had inadequate response at 30 minutes but adequate response at 60 minutes, 5 (1.4%) had adequate response at 30 minutes but inadequate response at 60 minutes. Using 60-minute cortisol alone was found to have a sensitivity of 98.1% and specificity of 100%, with 100% positive predictive value and 95.1% negative predictive value.

Conclusion

Probability of overdiagnosis of AI is significantly higher if only 30-minute cortisol were to be considered without the 60-minute cortisol. This study highlights the importance of measuring the 60-minute cortisol value to avoid misclassification of AI.

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