Harmonization of Glutamic Acid Decarboxylase and Islet antigen-2 Autoantibody Assays for National Institute of Diabetes and Digestive and Kidney Diseases Consortia

J Clin Endocrinol Metab. 2010 Jul;95(7):3360-7. doi: 10.1210/jc.2010-0293. Epub 2010 May 5.

Abstract

Background/rationale: 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).

Conclusion: 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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Academies and Institutes
  • Adolescent
  • Adult
  • Autoantibodies / immunology*
  • Glutamate Decarboxylase / immunology*
  • Humans
  • Radioligand Assay / methods*
  • Receptor-Like Protein Tyrosine Phosphatases, Class 8 / immunology*
  • Reference Values
  • Sensitivity and Specificity

Substances

  • Autoantibodies
  • Receptor-Like Protein Tyrosine Phosphatases, Class 8
  • Glutamate Decarboxylase