Bobby V. Li¹, Amas K. H. Lee¹, Robert C. W. Hawkins¹

¹Department of Laboratory Medicine, Tan Tock Seng Hospital, Singapore, Singapore

Background: Short Synacthen tests are performed to exclude adrenal insufficiency. However, baseline ACTH measurement is not universal. This study evaluated the value of baseline ACTH in Synacthen tests. 

Methods: Synacthen tests from April 2023-Jan 2024 with baseline from 6-10 am were identified. Plasma cortisol was measured by Beckman Coulter DxI800; ACTH by Roche e601. The proportion of baseline ACTH within and outside the morning reference interval (RI) (2-14 pmol/L) was determined, and split based on the 30-minute cortisol (COR30<420 nmol/L) threshold for inadequate response from ESA/AACB/RCPA Harmonization of Endocrine Dynamic Testing – Adult (HEDTA). 

Results: Baseline ACTH was available in 270/338 Synacthen tests [162/186 Endocrinology (100% outpatient), 53/70 General Medicine (96% inpatient), 55/82 other]. For COR30<420 nmol/L (n=60); baseline ACTH<2 pmol/L: 15%, ACTH 2-14 pmol/L: 58%, ACTH>14 pmol/L: 27%. For COR30≥420 nmol/L (n=210); baseline ACTH<2 pmol/L: 5%, ACTH 2-14 pmol/L: 90%, ACTH>14 pmol/L: 5% (p<0.001). Six patients with ACTH≥23 pmol/L all had COR30<420 nmol/L.

Conclusions: The proportion of ACTH outside RI was higher in presence of inadequate post-Synacthen cortisol response (42% vs 10%), demonstrating utility in classifying as primary or secondary adrenal insufficiency in an Asian population. It was noted that higher proportions of Endocrinology requests had baseline ACTH measured.

The work is the presenting author's original idea.