Harmonization of glutamic acid decarboxylase and islet antigen-2 autoantibody assays for national institute of diabetes and digestive and kidney diseases consortia.
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.
Bonifacio
Ezio
E
Deutsche Forschungsgemeinschaft Center for Regenerative Therapies, 01307 Dresden, Germany. ezio.bonifacio@crt-dresden.de
Yu
Liping
L
Williams
Alastair K
AK
Eisenbarth
George S
GS
Bingley
Polly J
PJ
Marcovina
Santica M
SM
Adler
Kerstin
K
Ziegler
Anette G
AG
Mueller
Patricia W
PW
Schatz
Desmond A
DA
Krischer
Jeffrey P
JP
Steffes
Michael W
MW
Akolkar
Beena
B
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
D001323:Autoantibodies; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D005968:Glutamate Decarboxylase
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