title: [Diagnosis of pheochromocytoma and paraganglioma: the clonidine suppression test in patients with borderline elevations of plasma free normetanephrine].
abstract: BACKGROUND
  Measurements of plasma free metanephrines provide a sensitive test for the diagnosis of pheochromocytoma/paraganglioma (P/PGL), with highly elevated levels diagnostic of the disease. However, there is less diagnostic certainty in patients with mild elevations of these catecholamine metabolites.
  
  
  METHODS
  Here we report use of the clonidine suppression test (CST) as a second-tier diagnostic test in 24 patients with mild elevations of plasma free metanephrines and/or catecholamines. Blood samples before and 3 hours after clonidine were analyzed for plasma concentrations of metanephrines and catecholamines with a negative test result defined as either a clonidine-induced fall in normetanephrine or noradrenaline by more than 40 % and 50 % respectively or to below the upper cut-offs of reference intervals.
  
  
  RESULTS
  P/PGLs were confirmed in 9 patients and excluded in 15 by independent criteria. More than half of the patients without P/PGL showed normalized plasma concentrations of normetanephrine at baseline before clonidine compared to initial screening; all showed appropriate clonidine-induced falls in normetanephrine and noradrenaline or levels after the drug below upper cut-offs, indicating a diagnostic specificity of 100 % (CI 78-100 %). However, similar responses for noradrenaline were noted in 7 patients with P/PGL, indicating a diagnostic sensitivity of only 22 % (CI 2,8-60 %) compared to 100 % (CI 66-100 %) for normetanephrine.
  
  
  CONCLUSIONS
  These results support use of the CST in combination with measurements of normetanephrine for confirming or excluding P/PGL in patients with borderline elevated test results, which should, however, first be confirmed by sampling blood under standardized resting conditions.
authors.affiliation: Medizinische Klinik III, UniversitätsklinikumCarl Gustav Carus der Technischen Universität Dresden.
authors.forename: R
authors.initials: R
authors.lastname: Därr
authors.forename: J W
authors.initials: JW
authors.lastname: Lenders
authors.forename: K
authors.initials: K
authors.lastname: Stange
authors.forename: B
authors.initials: B
authors.lastname: Kindel
authors.forename: L C
authors.initials: LC
authors.lastname: Hofbauer
authors.forename: S R
authors.initials: SR
authors.lastname: Bornstein
authors.forename: G
authors.initials: G
authors.lastname: Eisenhofer
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000097:blood* / Q000175:diagnosis*; D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D003000:Clonidine; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009647:Normetanephrine / Q000097:blood*; D010673:Pheochromocytoma / Q000097:blood* / Q000175:diagnosis*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; D009647:Normetanephrine; D003000:Clonidine