Endocrine Abstracts

JOINT1600

Background: The short Synacthen test (SST), also known as the ACTH (cosyntropin) stimulation test, is widely used to assess adrenal function. Its utilization and performance, however, is not universally standardized. The Department of Endocrinology at Singapore General Hospital has a dedicated outpatient SST service for evaluation and follow-up of patients with suspected or confirmed adrenal insufficiency.

Objective: This study aims to evaluate the utilization patterns and outcomes of SSTs performed at an endocrine unit in a tertiary hospital.

Methods: A retrospective audit of SST data is conducted for patients tested between 8 August 2024 and 7 January 2025. The choice of low-dose 1 mg SST (LD-SST) or standard-dose 250 mg SST (SD-SST) is based on the ordering endocrinologist’s clinical discretion. In general, LD-SST is typically preferred for patients with suspected central adrenal insufficiency, while SD-SST is performed for all other indications. A peak stimulated cortisol of ≥ 500 nmol/l is considered as an adequate adrenal response.

Results: One hundred and seventy-eight SSTs were performed during the study period. All tests were completed successfully. The majority (n =120, 67%) were LD-SSTs, and the remaining (n =58, 33%) being SD-SSTs. Adequate adrenal responses were observed in 56% (n =67) of LD-SSTs and 64% (n =37) of SD-SSTs. All except 2 patients listed for LD- SST had known or suspected hypothalamic/pituitary diseases (n =118, 98%), including pituitary macroadenoma (n =65), pituitary microadenoma (n =20), suprasellar meningioma (n =4), Rathke cleft cyst (n =4), empty sella syndrome (n =3), clival chordoma (n =2), lymphocytic hypophysitis (n =1), prior cranial irradiation (n =7), biochemical abnormalities resembling central hypothyroidism (n =10) and central AVP deficiency (n =1). The most common indication for standard-dose SST was for the diagnosis or follow-up of adrenal insufficiency in patients receiving exogenous glucocorticoids (n =32, 55%). The remaining patients had clinical presentations suggestive of adrenal insufficiency (n =18), hypothalamic/pituitary diseases (n =4), suspected congenital adrenal hyperplasia (n =3) and possible autoimmune polyglandular syndrome (n =1). There were no immediate complications or adverse events following all SSTs.

Conclusion: SST is a useful and relatively easy-to-perform dynamic endocrine test in the evaluation of adrenal function. Most cases were evaluated in the context of possible central adrenal insufficiency due to hypothalamic/pituitary pathology. The high demand for outpatient SST highlights its importance in clinical practice.