title: Determination of 21-hydroxylase autoantibodies: inter-laboratory concordance in the Euradrenal International Serum Exchange Program.
abstract: BACKGROUND
  21-Hydroxylase autoantibodies (21OHAb) are markers of an adrenal autoimmune process that identifies individuals with autoimmune Addison's disease (AAD). Quality and inter-laboratory agreement of various 21OHAb tests are incompletely known. The objective of the study was to determine inter-laboratory concordance for 21OHAb determinations.
  
  
  METHODS
  Sixty-nine sera from 51 patients with AAD and 51 sera from 51 healthy subjects were blindly coded by a randomization center and distributed to 14 laboratories that determined 21OHAb, either by an "in-house" assay (n=9) using in vitro-translated (35)S-21OH or luciferase-labeled 21OH or a commercial kit with (125)I-21OH (n=5). Main outcome measures were diagnostic accuracy of each participating laboratory and inter-laboratory agreement of 21OHAb assays.
  
  
  RESULTS
  Intra-assay coefficient of variation ranged from 2.6% to 5.3% for laboratories using the commercial kit and from 5.1% to 23% for laboratories using "in-house" assays. Diagnostic accuracy, expressed as area under ROC curve (AUC), varied from 0.625 to 0.947 with the commercial kit and from 0.562 to 0.978 with "in-house" methods. Cohen's κ of inter-rater agreement was 0.603 among all 14 laboratories, 0.691 among "in-house" laboratories, and 0.502 among commercial kit users. Optimized cutoff levels, calculated on the basis of AUCs, increased the diagnostic accuracy of every laboratory (AUC >0.9 for 11/14 laboratories) and increased the Cohen's κ of inter-rater agreement. Discrepancies in quantitation of 21OHAb levels among different laboratories increased with increasing autoantibody levels.
  
  
  CONCLUSIONS
  The quality of 21OHAb analytical procedures is mainly influenced by selection of cutoff value and correct handling of assay materials. A standardization program is needed to identify common standard sera and common measuring units.
authors: Alberto
authors: A
authors: Falorni
authors: Vittorio
authors: V
authors: Bini
authors: Corrado
authors: C
authors: Betterle
authors: Annalisa
authors: A
authors: Brozzetti
authors: Luis
authors: L
authors: Castaño
authors: Marta
authors: M
authors: Fichna
authors: Olle
authors: O
authors: Kämpe
authors: Gunnar
authors: G
authors: Mellgren
authors: Pärt
authors: P
authors: Peterson
authors: Shu
authors: S
authors: Chen
authors: Johan
authors: J
authors: Rönnelid
authors: Jochen
authors: J
authors: Seissler
authors: Claudio
authors: C
authors: Tiberti
authors: Raivo
authors: R
authors: Uibo
authors: Liping
authors: L
authors: Yu
authors: Åke
authors: Å
authors: Lernmark
authors: Eystein
authors: E
authors: Husebye
mesh_terms: D000224:Addison Disease / Q000097:blood* / Q000201:enzymology / Q000276:immunology; D000328:Adult; D001323:Autoantibodies / Q000097:blood* / Q000276:immunology*; D015415:Biomarkers / Q000097:blood; D005260:Female; D006801:Humans; D007753:Laboratories / Q000592:standards; D059021:Laboratory Proficiency Testing / Q000592:standards; D008297:Male; D008875:Middle Aged; D013255:Steroid 21-Hydroxylase / Q000276:immunology*; D055815:Young Adult
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; D013255:Steroid 21-Hydroxylase