title: Preanalytical validation and reference values for a mass spectrometric assay of serum vanillylmandelic acid for screening of catecholamine secreting neuroendocrine tumors.
abstract: BACKGROUND
  Urinary vanillylmandelic acid (VMA) is used to diagnose and monitor catecholamine secreting neuroendocrine tumors (NETs). We developed and validated a new liquid chromatography tandem mass spectrometry (LC-MS/MS) assay for determination of serum VMA.
  
  
  METHODS
  We used serum samples from healthy volunteers (n=314) and patients suspected for NET (n=36). Deuterated VMA as an internal standard was added to samples before solid phase extraction (SPE) and LC-MS/MS analysis. We studied the effects of sample storage, sampling device and a meal on serum VMA and metanephrine concentrations. Diurnal variation and age-dependent reference intervals were established. The diagnostic performance was compared with a urinary HPLC assay for VMA and metanephrines and a serum metanephrine LC-MS/MS assay.
  
  
  RESULTS
  Serum VMA is stable at least for one day at +4°C, seven days at room temperature and 98 days at -20°C. Type of sampling device was not critical, but elevated serum VMA occurs after a meal (p = 0.031). Serum VMA increased with age. Therefore, we suggest clinical cut-off values of 62 nmol/L, 80 nmol/L and 108 nmol/L for age groups 18-50 yrs, 51-70 yrs and > 70 yrs, respectively. Comparison between a urinary VMA HPLC assay and serum VMA LC-MS/MS assay showed good correlation.
  
  
  CONCLUSIONS
  Our LC-MS/MS assay is fast and sensitive and suits well for use in a clinical laboratory. Compared to 24-h urine collection our serum assay enables well controlled sampling and convenient preanalytical steps.
authors.affiliation: Haartman Institute, University of Helsinki, Finland; HUSLAB, Helsinki University Central Hospital, Helsinki, Finland. Electronic address: niina.tohmola@helsinki.fi.
authors.forename: Niina
authors.initials: N
authors.lastname: Tohmola
authors.affiliation: HUSLAB, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Outi
authors.initials: O
authors.lastname: Itkonen
authors.affiliation: HUSLAB, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Ursula
authors.initials: U
authors.lastname: Turpeinen
authors.affiliation: Haartman Institute, University of Helsinki, Finland.
authors.forename: Sakari
authors.initials: S
authors.lastname: Joenväärä
authors.affiliation: Haartman Institute, University of Helsinki, Finland; HUSLAB, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Risto
authors.initials: R
authors.lastname: Renkonen
authors.affiliation: HUSLAB, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Esa
authors.initials: E
authors.lastname: Hämäläinen
mesh_terms: D000236:Adenoma / Q000097:blood* / Q000175:diagnosis / Q000652:urine; D000293:Adolescent; D000310:Adrenal Gland Neoplasms / Q000097:blood* / Q000175:diagnosis / Q000652:urine; D000328:Adult; D000368:Aged; D001681:Biological Assay; D014408:Biomarkers, Tumor / Q000097:blood* / Q000652:urine; D016022:Case-Control Studies; D002853:Chromatography, Liquid; D005260:Female; D006801:Humans; D008297:Male; D008676:Metanephrine / Q000097:blood / Q000652:urine; D008875:Middle Aged; D009447:Neuroblastoma / Q000097:blood* / Q000175:diagnosis / Q000652:urine; D010235:Paraganglioma / Q000097:blood* / Q000175:diagnosis / Q000652:urine; D012016:Reference Values; D012680:Sensitivity and Specificity; D053719:Tandem Mass Spectrometry; D014642:Vanilmandelic Acid / Q000097:blood* / Q000652:urine
chemical_list: D014408:Biomarkers, Tumor; D008676:Metanephrine; D014642:Vanilmandelic Acid
keywords: LC–MS/MS; Metanephrines; Neuroblastoma; Paraganglioma; Pheochromocytoma; Vanillylmandelic acid