title: Plasma-free vs deconjugated metanephrines for diagnosis of phaeochromocytoma.
abstract: BACKGROUND
  The diagnosis of phaeochromocytoma is commonly performed by the measurements of plasma-free normetanephrine and metanephrine. Plasma-deconjugated normetanephrine and metanephrine have been proposed as alternative, equivalent, but easier to measure biomarkers.
  
  
  OBJECTIVE
  The aim of this study was to compare the diagnostic performance of plasma-free vs deconjugated normetanephrine and metanephrine in patients tested for phaeochromocytoma.
  
  
  METHODS
  The study population included a reference group of 262 normotensive and hypertensive volunteers, 198 patients with phaeochromocytoma and 528 patients initially suspected of having the tumour, but with negative investigations after at least 2 years of follow-up. Measurements were performed using liquid chromatography with electrochemical detection.
  
  
  RESULTS
  Plasma concentrations of free normetanephrine were 17-fold higher in patients with phaeochromocytoma than in the reference population, a 72% larger (P < 0·001) difference than that for the 10-fold higher levels of plasma-deconjugated normetanephrine. In contrast, relative increases in plasma concentrations of free and deconjugated metanephrine were similar. Using upper cut-offs established in the reference population, measurements of plasma-free metabolites provided superior diagnostic performance than deconjugated metabolites according to measures of both sensitivity (97% vs 92%, P = 0·002) and specificity (93% vs 89%, P = 0·012). The area under the receiver operating characteristic curve for the free metabolites was larger than that for the deconjugated metabolites (0·986 vs 0·965, P < 0·001).
  
  
  CONCLUSIONS
  Measurements of plasma-free normetanephrine and metanephrine are superior to the deconjugated metabolites for diagnosis of phaeochromocytoma.
authors: Institute of Clinical Chemistry and Laboratory Medicine, University Hospital Carl Gustav Carus at the TU Dresden, Fetscherstrasse 74, Dresden, Germany. Christina.Pamporaki@uniklinikum-dresden.de
authors: Christina
authors: C
authors: Pamporaki
authors: Roland
authors: R
authors: Därr
authors: Michael
authors: M
authors: Bursztyn
authors: Stephan
authors: S
authors: Glöckner
authors: Stefan R
authors: SR
authors: Bornstein
authors: Jacques W M
authors: JW
authors: Lenders
authors: Karel
authors: K
authors: Pacak
authors: Axel
authors: A
authors: Krinner
authors: Graeme
authors: G
authors: Eisenhofer
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000097:blood / Q000150:complications / Q000175:diagnosis*; D000328:Adult; D014408:Biomarkers, Tumor / Q000097:blood; D002853:Chromatography, Liquid; D055664:Electrochemical Techniques; D005260:Female; D006801:Humans; D006973:Hypertension / Q000097:blood / Q000150:complications; D008297:Male; D008676:Metanephrine / Q000097:blood*; D009647:Normetanephrine / Q000097:blood*; D010673:Pheochromocytoma / Q000097:blood / Q000150:complications / Q000175:diagnosis*; D012372:ROC Curve; D055815:Young Adult
chemical_list: D014408:Biomarkers, Tumor; D009647:Normetanephrine; D008676:Metanephrine