title: European specialist porphyria laboratories: diagnostic strategies, analytical quality, clinical interpretation, and reporting as assessed by an external quality assurance program.
abstract: BACKGROUND
  The porphyrias are a group of rare metabolic disorders whose diagnosis depends on identification of specific patterns of porphyrin precursor and porphyrin accumulation in urine, blood, and feces. Diagnostic tests for porphyria are performed by specialized laboratories in many countries. Data regarding the analytical and diagnostic performance of these laboratories are scarce.
  
  
  METHODS
  We distributed 5 sets of multispecimen samples from different porphyria patients accompanied by clinical case histories to 18-21 European specialist porphyria laboratories/centers as part of a European Porphyria Network organized external analytical and postanalytical quality assessment (EQA) program. The laboratories stated which analyses they would normally have performed given the case histories and reported results of all porphyria-related analyses available, interpretative comments, and diagnoses.
  
  
  RESULTS
  Reported diagnostic strategies initially showed considerable diversity, but the number of laboratories applying adequate diagnostic strategies increased during the study period. We found an average interlaboratory CV of 50% (range 12%-152%) for analytes in absolute concentrations. Result normalization by forming ratios to the upper reference limits did not reduce this variation. Sixty-five percent of reported results were within biological variation-based analytical quality specifications. Clinical interpretation of the obtained analytical results was accurate, and most laboratories established the correct diagnosis in all distributions.
  
  
  CONCLUSIONS
  Based on a case-based EQA scheme, variations were apparent in analytical and diagnostic performance between European specialist porphyria laboratories. Our findings reinforce the use of EQA schemes as an essential tool to assess both analytical and diagnostic processes and thereby to improve patient care in rare diseases.
authors.affiliation: Norwegian Porphyria Centre (NAPOS), Laboratory of Clinical Biochemistry, Haukeland University Hospital, Bergen, Norway.
authors.forename: Aasne K
authors.initials: AK
authors.lastname: Aarsand
authors.forename: Jørild H
authors.initials: JH
authors.lastname: Villanger
authors.forename: Egil
authors.initials: E
authors.lastname: Støle
authors.forename: Jean-Charles
authors.initials: JC
authors.lastname: Deybach
authors.forename: Joanne
authors.initials: J
authors.lastname: Marsden
authors.forename: Jordi
authors.initials: J
authors.lastname: To-Figueras
authors.forename: Mike
authors.initials: M
authors.lastname: Badminton
authors.forename: George H
authors.initials: GH
authors.lastname: Elder
authors.forename: Sverre
authors.initials: S
authors.lastname: Sandberg
mesh_terms: D000293:Adolescent; D000368:Aged; D015415:Biomarkers / Q000032:analysis; D002675:Child, Preschool; D019411:Clinical Laboratory Techniques / Q000592:standards*; D005060:Europe; D005260:Female; D006801:Humans; D007391:International Cooperation; D008297:Male; D008875:Middle Aged; D011164:Porphyrias / Q000175:diagnosis*; D011166:Porphyrins / Q000032:analysis; D011786:Quality Control; D012015:Reference Standards; D012107:Research Design
chemical_list: D015415:Biomarkers; D011166:Porphyrins