The clinical diagnosis of Cushing's syndrome must be confirmed biochemically. The measurement of urinary free cortisol is considered the diagnostic test of choice for establishing the presence or absence of endogenous hypercortisolism. Carbamazepine (CBZ) is a tricyclic agent with therapeutic efficacy in a broad range of conditions and has been shown to influence the hypothalamic-pituitary-adrenal axis in both humans and experimental animals. CBZ may induce hepatic microsomal drug metabolizing enzymes and enhance the metabolic clearance of dexamethasone, causing a false positive dexamethasone suppression test. This report documents another problem with CBZ in the evaluation of patients with suspected hypercortisolism. We describe three patients taking CBZ with spurious elevations of urine free cortisol when measured by high performance liquid chromatography (HPLC). One patient underwent an unnecessary inferior petrosal sinus ACTH sampling (IPSS) and another patient had been referred for IPSS. All three patients eventually were discovered to be eucortisolemic when urine free cortisol was measured by radioimmunoassay. This report provides evidence that a metabolite of CBZ interferes with the accurate measurement of urinary free cortisol when measured by HPLC.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism