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Diagnostic performance of morning serum cortisol as an alternative to short synacthen test for the assessment of adrenal reserve; a retrospective study
  1. Rajeev Kumar1,
  2. Peter Carr2,
  3. Ws Wassif3
  1. 1 Diabetes and Endocrinology, Bedford Hospital NHS Trust, Bedford, UK
  2. 2 Statistical Analyst, The Alan Turing Institute, London, UK
  3. 3 Clinical Biochemistry, Bedford Hospital NHS Trust, Bedford, UK
  1. Correspondence to Rajeev Kumar, Consultant Physician and Endocrinologist, Bedford Hospital, Bedford, UK;Rajeev.kumar{at}


Objective The short synacthen test (SST) is widely used across the UK to assess adrenal reserve. The main objective of our study was to determine the morning serum cortisol level that will predict adrenal insufficiency (AI) thus reducing our reliance on SST.

Design This was a single centre retrospective study of 393 SST tests measuring 0 and 60 min cortisol levels after administration of 250 μg of synacthen (synthetic ACTH).

Patients and methods All the SST tests for patients suspected of primary or secondary AI between April 2016 and October 2018 were included in this study. We used serum to determine circulating cortisol by a newer generation competitive electrochemiluminescence immunoassay (ECLIA) (Roche Diagnostics). A post-ACTH cortisol response of ≥420 nmol/L at 60 min was considered adequate to rule out AI. The data were analysed to ascertain the relationship between 0 min and 60 min serum cortisol.

Results A total of 393 SST results were included in this study. Overall, a total of 332 (84.5%) subjects achieved sufficient serum cortisol level at 60 min, while 61 subjects (15.5%) showed insufficient response. Using the logistic regression, we determined that a morning basal serum cortisol level of ≥354 nmol/L was able to predict normal adrenal function with 100% sensitivity. We were unable to find a lower cut-off value below which SST will not be required. By using this proposed cut-off point, approximately 37% of the SSTs tests could be avoided.

Conclusions Basal morning serum cortisol can be safely used as a first step in the evaluation of patients with suspected AI. This will enhance the number of patients being screened for this condition.

  • Diabetes & endocrinology
  • Adrenal disorders
  • Clinical pharmacology

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  • Contributors RK contributed to the conception and design of the study, and wrote the first draft. PC performed and wrote the statistical analysis. WW contributed to the conception and design of the study, and the writing of the article. All authors have given their approval for the final version of the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests All authors have completed the ICMJE uniform disclosure form at and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted wor.

  • Patient consent for publication Not required.

  • Ethics approval After careful consideration, we decided not to seek patient consent or ethical approval as the data collection was retrospective and all data was completely anonymised.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement All the authors of this study do commit to making the relevant anonymised patient-level data available on reasonable request.

  • Dissemination declaration Dissemination of study results to study participants and/or patient organisations is not applicable.