Background: Determining post-operative remission in Cushings disease is challenging. There is no consensus for the post-operative serum cortisol value which reliably predicts remission of Cushings disease following trans-sphenoidal surgery. Traditionally, an early post-operative serum cortisol of below 50 nmol/L has been used to predict remission, but achieving this is often at the expense of hypopituitarism.
Objective: To identify whether post-operative day five 9AM serum cortisol is an accurate predictor of remission following trans-sphenoidal surgery for Cushings disease.
Methods: Post-operative day five 9AM serum cortisol data were retrospectively reviewed for 39 trans-sphenoidal surgeries for Cushings disease (January 2006 to April 2017). The day of trans-sphenoidal surgery was designated post-operative day one. Post-operative glucocorticoid replacement was omitted for 1824 hours prior to sampling. Remission was defined as an absence of clinical or biochemical evidence of hypercortisolism for at least six months and up to five years post-operatively.
Results: The remission rate was 69.2% (27/39). Area under the receiver operating characteristic curve for post-operative day five 9AM serum cortisol as a predictor of remission of Cushings disease following trans-sphenoidal surgery was 0.98 (95% CI 0.94 1.02). A cut-off of 195 nmol/L provided the highest sensitivity (100%) and specificity (92.6%) with a positive predictive value (PPV) of 85.7% and negative predictive value (NPV) of 100%. In contrast, using the traditional cut-off of 50 nmol/L produced 100% sensitivity, 51.9% specificity, 48% PPV and 100% NPV.
Conclusions: Post-operative day five 9AM serum cortisol is a reliable predictor of remission of Cushings disease. A cut-off of 195 nmol/L for serum cortisol yielded the greatest diagnostic accuracy of remission of Cushings disease for up to five years following trans-sphenoidal surgery. The traditional cut-off of less than 50 nmol/L was less reliable at predicting remission.