Improving the Interpretation of Afternoon Cortisol Levels and SSTs to Prevent Misdiagnosis of Adrenal Insufficiency

Vijay Ramadoss; Katharine Lazarus; Andrew Toby Prevost; Tricia Tan; Karim Meeran; Sirazum Choudhury


J Endo Soc. 2021;5(11) 

In This Article

Abstract and Introduction


Background: Adrenal Insufficiency (AI), especially iatrogenic-AI, is a treatable cause of mortality. The difficulty in obtaining 9 AM cortisol levels means samples are taken at suboptimal times, including a substantial proportion in the afternoon. Low afternoon cortisol levels often provoke short Synacthen tests (SSTs). It is important that this does not lead to patients misdiagnosed with AI, exposing them to the excess mortality and morbidity of inappropriate steroid replacement therapy.

Methods: This retrospective study collected 60 178 cortisol results. Medical records, including subsequent SSTs of initial cortisol results measured after midday were reviewed.

Results: Receiver operating characteristic analysis (area under the curve: 0.89) on 6531 suitable cortisol values showed that a limit of <201.5 nmol/L achieved a sensitivity and specificity of 95.6% and 72.6%, while a limit of <234 nmol/L had a sensitivity of 100% and a specificity of 59.5%. Out of 670 SSTs, 628 patients passed. Of these, 140 would have otherwise failed if only their 30-min cortisol was assessed without the 60-min value. A 30- and 60-min SST cortisol cutoff of 366.5 nmol/L and 418.5 nmol/L, respectively, can achieve a sensitivity of >95% on the Abbott analyser platform.

Conclusion: An afternoon cortisol >234 nmol/L excludes AI on Abbott analyser platforms. In patients who have an afternoon cortisol <234 nmol/L, including both 30- and 60-min SST cortisol values prevents unnecessary glucocorticoid replacement therapy in 22.3% of individuals in this study. The Abbott analyser SST cortisol cutoffs used to define AI should be 366.5 nmol/L and 418.5 nmol/L at 30 and 60 min, respectively. All patients remained well subsequently with at least 1-year longitudinal follow-up.


Adrenal insufficiency (AI) is associated with an increased mortality, principally due to cardiovascular disease, malignancy, and infection.[1] There is growing evidence that this observation is fueled by excess glucocorticoid replacement from intrinsically suboptimal replacement regimens.[2–4] It is therefore important that patients are not incorrectly labeled with AI, thereby exposing them to inappropriate lifelong glucocorticoid replacement and the accompanying excess mortality and morbidity.

AI is a differential diagnosis that is commonly considered despite its rarity in a multitude of clinical presentations, especially as affected individuals can present with nonspecific signs and symptoms such as tiredness, weight loss, hypotension, nausea, and vomiting.[5] A study of 216 patients has demonstrated the significant difficulty physicians and patients face in establishing a diagnosis.[6] Over 50% of males and 70% of females in a German population took greater than 6 months to obtain a diagnosis, with 20% being diagnosed after 5 years and two thirds receiving a diagnosis only after having consulted 3 different physicians. It is important not to mislabel those who have nonspecific features as AI, but also important to correctly diagnose the rare patient with true AI, in whom appropriate glucocorticoid replacement therapy is lifesaving. A 9 AM cortisol should be requested in the first instance. A value of greater than 336 nmol/L (on Abbott platforms, but may vary according to different analyzers) suggests that a short Synacthen test (SST) using tetracosactide acetate is not required.[7]

There is often practical difficulty in obtaining 9 AM cortisol levels in patients. Demand for 9 AM phlebotomy slots can mean that some patients have to wait beyond the specified time. Blood tests are usually ordered after a physician review possibly in outpatient clinic in the afternoon, and patients may opt to be bled at the same time rather than experience the inconvenience of attending the hospital on a separate occasion the next morning. This often leads to cortisol samples being collected for analysis at inappropriate times, such as during late morning phlebotomy rounds in admissions to hospital or in the afternoon at outpatient clinic settings. While morning cortisol levels have been rigorously studied in the diagnosis of AI,[8–10] there is currently no harmonized reference interval for an untimed cortisol level, and it is unlikely that one will be ever be defined. The observed tendency to order SSTs on the basis of afternoon cortisol results in the present study is likely to stem from concern about missing patients with undiagnosed AI and subsequently missing a potential adrenal crisis. Although the accepted practice of performing an early morning cortisol should be the first step and can preclude the need for a formal SST,[5] many patients find it more convenient to complete the SST instead of having further blood tests on another occasion. There is no evidence that this practice has a significant impact on preventing adrenal crises and subsequent death in undiagnosed patients. Studies that stratify hospital admissions for crises consistently show increased incidences for those with primary AI over secondary AI, possibly because the former are unable to synthesize aldosterone.[11]

The act of performing afternoon cortisols may be driving the increasing number of SSTs performed, when low cortisol results are returned. As the interpretation of SSTs is largely unchanged since the 1960s despite advances in assay techniques, this tendency to overinvestigate with SSTs will in turn lead to more failed SSTs and apparent increase in AI prevalence. This is especially problematic in patients with an otherwise low index of suspicion for AI in the context of equivocal afternoon cortisol results. The consequence of this is the misdiagnosis of patients with AI and the subsequent excess risk of mortality in this population.

A recent retrospective analysis of 2700 patients demonstrated that an afternoon cortisol value cutoff value of less than 250 nmol/L correlated with suboptimal SST outcomes and achieved over 96% sensitivity and 37.7% specificity in subsequent diagnosis of AI.[12] In practice, this cutoff does not account for the number of false positives, which in turn may still lead to a large number of unnecessary confirmatory SST tests. At present, at Imperial College Healthcare National Health Service (NHS) Trust, an afternoon value of less than 100 nmol/L is labeled as a "critical result" and prompts a review by our biochemistry department with the prospect of a further call-out to a clinician as per Royal College of Pathology guidelines and International Organisation for Standardization (ISO) 15189 standards.[13,14] Many of these "critical results" lead to investigation and no subsequent evidence for AI. The aim of this study was to clarify the diagnostic utility of cortisol levels taken in patients after midday.