Endocrine Abstracts

Introduction: A short-synacthen test (SST) is routinely used to diagnose hypoadrenalism, however, some authors suggest using morning serum cortisol as an initial screening test to rule out hypoadrenalism. We assessed the utility of a morning cortisol as a screening test when compared with the outcome of SST.

Methods: We retrospectively analysed SSTs carried out in our endocrine outpatient clinic in the last 3 years (649 results). Of these, 113 were identified as morning tests. We evaluated baseline morning cortisol values against stimulated values, using a cut-off ≥550 nmol/l to indicate a normal test. For step-wise values of morning cortisol, we calculated the sensitivity and specificity of its use as a screening test. Due to the clinical consequence of missing a diagnosis of hypoadrenalism it was felt that a screening cortisol value would only be useful if it excluded all positive tests.

Results: Of 113 morning SSTs (109 patients, 49 males, median age 48 years), 13 confirmed hypoadrenalism. Analysing these, a morning baseline cortisol ≥450 nmol/l ruled out all patients with hypoadrenalism and a morning cortisol level <100 mmol/l was diagnostic for hypoadrenalism. Twenty-eight patients had a baseline morning serum cortisol ≥450 nmol/l, 83 patients between 100 and 450 nmol/l, and two patients ≤100 nmol/l. Using a morning cortisol cut-off ≥450 nmol/l as a screening test had a sensitivity of 100.0% and a specificity of 28.0%. The positive and negative predictive values were 15.3 and 100.0% respectively. By using a morning cortisol ≥450 nmol/l as a screening test, the number of short-synacthen tests we perform would be cut down by one quarter.

Conclusions: A morning cortisol result ≥450 nmol/l rules out hypoadrenalism with sensitivity of 100.0%. As the majority of morning cortisol tests would need to be re-evaluated with a SST, leading to potential delays in diagnosis of hypoadrenalism, a morning cortisol is of limited value as a screening test.