The Role of the Short Synacthen Test in the Diagnostic Evaluation of Hyponatremia: Insights from a Service Evaluation

Hyponatremia is a prevalent electrolyte disturbance, which has a multi-factorial aetiology, where adrenal insufficiency is a significant yet potentially under-identified cause. Synacthen test (SST) is a short test commonly used to assess adrenal gland function, but there is controversy over whether it should be routinely performed in all patients with hyponatremia. To determine the diagnostic value and clinical utility of the SST in hyponatremic patients to determine whether the regular use of SST is reasonable in practice. A prospective service assessment took place between November 2023 and June 2024 in two district general hospitals in the United Kingdom. One hundred and fifty-five patients who had undergone SST were used. Electronic health records were used to gather data regarding referral indications, clinical presentation, baseline biochemical parameters, and SST outcomes. The effects of potential confounding variables, such as corticosteroid and oestrogen therapy, were also examined. The indications of referral were heterogeneous, with suspected adrenal pathology (47.1%), pituitary disorders (13.6), and cortisol imbalance (11.0) in the first place. A total of 38.7% of patients had an abnormal SST outcome that agreed with adrenal insufficiency, and 54.8% had a normal adrenal response. The rest of the cases were indeterminate. The effects of medication and lack of full baseline hormonal evaluation were widespread and led to interpretation difficulties. The high percentage of adverse outcomes is an indication of possible overuse of SST among unselected patients. The SST continues to be a useful confirmatory test in patients suspected of having adrenal insufficiency and an endocrine etiology of hyponatremia.