Urinary clonidine suppression testing for the diagnosis of pheochromocytoma

Objective: The diagnosis of pheochromocytoma/paraganglioma (PPGL) involves detection of elevated levels of plasma and/or 24-h urine catecholamines and/or their metabolites, including metanephrines. Although these tests are reasonably sensitive, false-positive results are often encountered. Follow-up tests can provide additional information to correctly diagnose PPGL. In this regard, the utility of the urinary clonidine suppression test (UCST) remains unknown. Methods: To assess the diagnostic accuracy of the UCST in confirming or excluding PPGL, we conducted a retrospective analysis of all patients who underwent a UCST between 2000 and 2013 (n59; 15 PPGLs) at a single centre. Twelve-hour urine catecholamines and metanephrines were assessed before and after clonidine administration, and examined in relation to final diagnosis, PPGL or non-PPGL. Receiver operating characteristic analyses were used to identify optimal positivity cut-offs. Sensitivity, specificity, positive and negative predictive values were calculated. Results: Clonidine significantly decreased urine creatininecorrected norepinephrine and normetanephrine in patients without PPGL (