title: Harmonization of glutamic acid decarboxylase and islet antigen-2 autoantibody assays for national institute of diabetes and digestive and kidney diseases consortia.
abstract: BACKGROUND
  Autoantibodies to islet antigen-2 (IA-2A) and glutamic acid decarboxylase (GADA) are markers for diagnosis, screening, and measuring outcomes in National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) consortia studies. A harmonization program was established to increase comparability of results within and among these studies.
  
  
  METHODS
  Large volumes of six working calibrators were prepared from pooled sera with GADA 4.8-493 World Health Organization (WHO) units/ml and IA-2A 2-235 WHO units/ml. Harmonized assay protocols for IA-2A and GADA using (35)S-methionine-labelled in vitro transcribed and translated antigens were developed based on methods in use in three NIDDK laboratories. Antibody thresholds were defined using sera from patients with recent onset type 1 diabetes and healthy controls. To evaluate the impact of the harmonized assay protocol on concordance of IA-2A and GADA results, two laboratories retested stored TEDDY study sera using the harmonized assays.
  
  
  RESULTS
  The harmonized assays gave comparable but not identical results in the three laboratories. For IA-2A, using a common threshold of 5 DK units/ml, 549 of 550 control and patient samples were concordantly scored as positive or negative, specificity was greater than 99% with sensitivity 64% in all laboratories. For GADA, using thresholds equivalent to the 97th percentile of 974 control samples in each laboratory, 1051 (97.9%) of 1074 samples were concordant. On the retested TEDDY samples, discordance decreased from 4 to 1.8% for IA-2A (n = 604 samples; P = 0.02) and from 15.4 to 2.7% for GADA (n = 515 samples; P < 0.0001).
  
  
  CONCLUSIONS
  Harmonization of GADA and IA-2A is feasible using large volume working calibrators and common protocols and is an effective approach to ensure consistency in autoantibody measurements.
authors.affiliation: Deutsche Forschungsgemeinschaft Center for Regenerative Therapies, 01307 Dresden, Germany. ezio.bonifacio@crt-dresden.de
authors.forename: Ezio
authors.initials: E
authors.lastname: Bonifacio
authors.forename: Liping
authors.initials: L
authors.lastname: Yu
authors.forename: Alastair K
authors.initials: AK
authors.lastname: Williams
authors.forename: George S
authors.initials: GS
authors.lastname: Eisenbarth
authors.forename: Polly J
authors.initials: PJ
authors.lastname: Bingley
authors.forename: Santica M
authors.initials: SM
authors.lastname: Marcovina
authors.forename: Kerstin
authors.initials: K
authors.lastname: Adler
authors.forename: Anette G
authors.initials: AG
authors.lastname: Ziegler
authors.forename: Patricia W
authors.initials: PW
authors.lastname: Mueller
authors.forename: Desmond A
authors.initials: DA
authors.lastname: Schatz
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Krischer
authors.forename: Michael W
authors.initials: MW
authors.lastname: Steffes
authors.forename: Beena
authors.initials: B
authors.lastname: Akolkar
mesh_terms: D000047:Academies and Institutes; D000293:Adolescent; D000328:Adult; D001323:Autoantibodies / Q000276:immunology*; D005968:Glutamate Decarboxylase / Q000276:immunology*; D006801:Humans; D011869:Radioligand Assay / Q000379:methods*; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8 / Q000276:immunology*; D012016:Reference Values; D012680:Sensitivity and Specificity
chemical_list: D001323:Autoantibodies; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D005968:Glutamate Decarboxylase
references.citation: Diabetes Care. 2008 Jan;31 Suppl 1:S55-60
references.pmid: 18165338
references.citation: J Clin Endocrinol Metab. 1996 Dec;81(12):4264-7
references.pmid: 8954025
references.citation: Ann N Y Acad Sci. 2008 Dec;1150:14-24
references.pmid: 19120262
references.citation: Diabetes. 1999 Mar;48(3):460-8
references.pmid: 10078544
references.citation: Ann N Y Acad Sci. 2008 Dec;1150:1-13
references.pmid: 19120261
references.citation: Pediatr Diabetes. 2007 Apr;8(2):74-87
references.pmid: 17448130
references.citation: J Med Genet. 2009 Jul;46(7):469-71
references.pmid: 19429597
references.citation: Control Clin Trials. 2004 Oct;25(5):458-71
references.pmid: 15465616
references.citation: Diabetologia. 2000 Oct;43(10):1282-92
references.pmid: 11079747
references.citation: Diabetes Care. 1999 Nov;22(11):1796-801
references.pmid: 10546010
references.citation: Diabetologia. 2008 May;51(5):846-52
references.pmid: 18373080
references.citation: Proc Natl Acad Sci U S A. 2007 Oct 23;104(43):17040-5
references.pmid: 17942684
references.citation: Diabetes. 1994 Aug;43(8):1005-9
references.pmid: 8039593
references.citation: Diabetes. 2003 May;52(5):1128-36
references.pmid: 12716742
references.citation: J Immunol Methods. 2009 Dec 31;351(1-2):75-9
references.pmid: 19837075
references.citation: Diabetes. 2003 Nov;52(11):2833-9
references.pmid: 14578303