Moderately impaired renal function increases morning cortisol and cortisol levels at dexamethasone suppression test in patients with incidentally detected adrenal adenomas

OBJECTIVE: Patients with incidentally detected adrenal adenomas may have subclinical hypercortisolism. We hypothesized that impaired renal function could lead to increased cortisol levels in these patients. DESIGN: Descriptive retrospective study of consecutive patients. PATIENTS: A total of 166 patients with incidentally detected unilateral adrenal adenomas were examined during 2008-2013. MEASUREMENTS: Levels of cortisol, ACTH and cortisol at 1 mg overnight dexamethasone suppression test (DST) were measured. The estimated glomerular filtration rate (eGFR) was calculated using the MDRD equation. RESULTS: Renal function was normal, mildly impaired, moderately impaired or severely impaired (eGFR >90, 60-90, 30-60 and 15-30 ml/min/1·73 m(2)) in 34, 54, 10 and 1% of the patients, respectively. Patients with normal and mildly impaired renal function had similar cortisol levels. Patients with moderately impaired renal function, compared to all the patients with eGFR >60 ml/min/1·73 m(2), exhibited increased cortisol (541 vs 456 nmol/l, P = 0·02), increased cortisol at DST (62 vs 37 nmol/l, P = 0·001), but similar ACTH levels (4·1 vs 2·9 pmol/l, P = 0·21). Patients with moderately impaired renal function thus exhibited cortisol at DST ≥ 50 nmol/l, more often than patients with eGFR >60 ml/min/1·73 m(2) (76% vs 30%, P = 0·000), while the prevalence of ACTH below 2 pmol/l was similar (24% vs 31%, P = 0·51). CONCLUSIONS: Moderately impaired renal function increases cortisol and cortisol at DST in patients with adrenal adenomas, while mildly impaired renal function has no such effect. Cortisol level at DST ≥ 50 nmol/l therefore seems to have low specificity in diagnosing subclinical adrenal hypercortisolism, and an additional criterion, for example low ACTH, is required.