Endocrine Abstracts

Introduction: The diagnosis of Cushing’s syndrome (CS) can be challenging and there is no single gold standard diagnostic test. Endocrinologists rely on a combination of plasma cortisol (before and after dexamethasone), midnight salivary cortisol and urinary free cortisol (UFC) to make the diagnosis. Assessment of urinary corticosteroids and their metabolites, measured by gas chromatography–mass spectrometry (GC–MS), provide a comprehensive picture of corticosteroid production, metabolism and excretion and so this may be a helpful additional diagnostic tool in CS.

Methods: We retrospectively examined the urinary steroid profiles assessed before and after a low-dose dexamethasone suppression test of 23 patients referred to our unit for further evaluation of possible CS. Patients were labelled as CS (n=10) or non-CS (n=13) by a consultant endocrinologist on the basis of clinical suspicion, UFC and post-dexamethasone plasma cortisol.

Results: Patients with CS demonstrated elevation only of glucocorticoid metabolites (tetrahydrocortisol (THF)/tetrahydrocortisone (THE)/allo THF/cortol and cortolone) with no significant suppression by dexamethasone. There was no difference in baseline steroid pattern between ACTH (n=6) and non ACTH (n=4) dependent CS. All urinary metabolites were within normal range in non-CS patients; glucocorticoids and mineralocorticoids (not androgens) were significantly suppressed after dexamethasone (P<0.03 in all cases). The only significant difference in urinary steroids between these groups was elevated post-dexamethasone glucocorticoid metabolites in CS subjects (P<0.03). Plasma cortisol correlated strongly with urinary total cortisol after dexamethasone suppression in both patient cohorts (P<0.01 in both groups).

Conclusions: Urinary steroid profiling using GC–MS provides no diagnostic advantage over conventional dexamethasone suppression testing+/−UFC in CS and should not be routinely performed in this setting. Whether it may help in subtype differentiation of CS requires further investigation. Currently, its use should remain limited to biochemical phenotyping of adrenal adenomas.