title: Synthetic calibrators for the analysis of total metanephrines in urine: revisiting the conditions of hydrolysis.
abstract: BACKGROUND
  The quantification of total (free+sulfated) metanephrines in urine is recommended to diagnose pheochromocytoma. Urinary metanephrines include metanephrine itself, normetanephrine and methoxytyramine, mainly in the form of sulfate conjugates (60-80%). Their determination requires the hydrolysis of the sulfate ester moiety to allow electrochemical oxidation of the phenolic group. Commercially available urine calibrators and controls contain essentially free, unhydrolysable metanephrines which are not representative of native urines. The lack of appropriate calibrators may lead to uncertainty regarding the completion of the hydrolysis of sulfated metanephrines, resulting in incorrect quantification.
  
  
  METHODS
  We used chemically synthesized sulfated metanephrines to establish whether the procedure most frequently recommended for commercial kits (pH 1.0 for 30 min over a boiling water bath) ensures their complete hydrolysis.
  
  
  RESULTS
  We found that sulfated metanephrines differ in their optimum pH to obtain complete hydrolysis. Highest yields and minimal variance were established for incubation at pH 0.7-0.9 during 20 min.
  
  
  CONCLUSIONS
  Urinary pH should be carefully controlled to ensure an efficient and reproducible hydrolysis of sulfated metanephrines. Synthetic sulfated metanephrines represent the optimal material for calibrators and proficiency testing to improve inter-laboratory accuracy.
authors.affiliation: Institute of Chemistry and Chemical Engineering, Ecole Polytechnique Fédérale de Lausanne, Batochime (Bat BCH), CH-1015 Lausanne, Switzerland.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Simonin
authors.forename: Sandrine
authors.initials: S
authors.lastname: Gerber-Lemaire
authors.forename: Catherine
authors.initials: C
authors.lastname: Centeno
authors.forename: Caroline
authors.initials: C
authors.lastname: Seghezzi
authors.forename: Katia
authors.initials: K
authors.lastname: Iglesias
authors.forename: Karim
authors.initials: K
authors.lastname: Abid
authors.forename: Eric
authors.initials: E
authors.lastname: Grouzmann
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000652:urine; D002138:Calibration; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008676:Metanephrine / Q000138:chemical synthesis / Q000737:chemistry* / Q000652:urine*; D010673:Pheochromocytoma / Q000652:urine; D013431:Sulfates / Q000737:chemistry; D035501:Uncertainty
chemical_list: D013431:Sulfates; D008676:Metanephrine