Pre-test Cortisol Levels in Predicting Short Synacthen Test Outcome: A Retrospective Analysis

Area of Science:

• Endocrinology
• Clinical Chemistry

Background:

• Short Synacthen tests (SSTs) are crucial for assessing adrenal function but are costly and resource-intensive.
• The availability of Synacthen and the need for supervision add to the challenges of widespread SST implementation.

Purpose of the Study:

• To evaluate the predictive value of pre-test cortisol (Cort0) levels for Short Synacthen test (SST) outcomes.
• To identify potential strategies for reducing the number of SSTs performed by utilizing pre-test measurements.

Main Methods:

• Retrospective analysis of 506 Short Synacthen tests (SSTs).
• Examination of pre-test cortisol (Cort0), indications, and timing of tests.
• Receiver Operating Characteristic (ROC) curve analysis to determine optimal Cort0 cut-off values for predicting SST outcomes in different testing time groups.

Main Results:

• Cort0 levels of ⩽124 nmol/L (Group 1) or ⩽47 nmol/L (Group 2) predicted SST failure with 100% specificity.
• Cort0 levels of ⩾314 nmol/L (Group 1) or ⩾323 nmol/L (Group 2) predicted a normal SST with 100% sensitivity.
• A significant correlation was found between Cort0 and 30-minute cortisol (r = 0.65–0.78, P < .001).
• Median Cort0 was significantly lower in patients with failed SSTs compared to those with normal results (147 vs 298 nmol/L, P < .001).

Conclusions:

• Pre-test cortisol levels can reliably predict normal SST outcomes, with specific cut-offs achieving 100% sensitivity.
• Implementing these pre-test cortisol cut-offs could potentially avoid 28.6% of SSTs, reducing costs and resource utilization.
• Further consideration of pre-test predictability is advised for patients with lower likelihoods of SST failure.