Sixty-minute post-Synacthen serum cortisol level: a reliable and cost-effective screening test for excluding adrenal insufficiency compared to the conventional short Synacthen test.

INTRODUCTION: Previous studies have indicated that most individuals reach peak cortisol levels in 60 minutes during the short Synacthen test (SST) done to exclude adrenal insufficiency. Therefore, measuring serum cortisol at only 60 minutes may suffice. This study was carried out to evaluate the significance of the 60-minute serum cortisol level in SST as a reliable and cost-effective screening test in comparison to the conventional SST.
METHODS: A cross-sectional study was conducted from January 2000 to September 2004, in which data was collected by reviewing medical records of all patients who underwent SST at the Aga Khan University Hospital, Karachi. A total of 236 patients suspected of having adrenal insufficiency were included. Values of serum cortisol at baseline, 30 and 60 minutes post-250 ug-injection Synacthen were recorded. The cortisol level was measured through fluorescence polarisation immunoassay. The cut-off value of 20 ug/dL was used to differentiate normal individuals from hypoadrenal individuals.
RESULTS: Out of 236 study participants, 93 (39 percent) were males and 143 (61 percent) were females. The mean age and standard deviation was 44.4 +/- 21 years. Cortisol concentration increased significantly from baseline to 30 minutes and 60 minutes after injecting Synacthen (p-value is less than 0.001 for each). The majority of the patients reached the cortisol peak of greater than 20 ug/dL (555 nmol/L) at 60 minutes. Normal responses were found in 148 patients (63.1 percent) at both 30 and 60 minutes, while 27 participants (12 percent) reached a peak greater than 20 ug/dL (555 nmol/L) at 60 minutes but were less than 20 ug/dL (555 nmol/L) at 30 minutes. In the deficient cases, SST showed abnormal responses in 60 cases (25 percent) at both 30 and 60 minutes. However, there was only one patient who reached a peak value of 21 ug/dL (589 nmol/L) at 30 minutes, which reduced to 17 ug/dL (485 nmol/L) at 60 minutes.
CONCLUSION: This study showed that a 60-minute cortisol value during SST was reliable enough in identifying normal subjects for excluding adrenal insufficiency, and was equally effective in identifying abnormal cases, as compared to values at both 30 and 60 minutes. It is therefore suggested that a single 60-minute post-Synacthen serum cortisol level may suffice, as compared to the conventional SST. This is also significant as a cost-effective measure, especially in third world countries where cost is a major issue for diagnosing and treating patients.