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Low agreement between radio binding assays in analyzing glutamic acid decarboxylase (GAD65Ab) autoantibodies in patients classified with type 2 diabetes

Daka, Bledar; Svensson, Maria K.; Lernmark, Åke LU ; Mincheva-Nilsson, Lucia; Hallmans, Goran and Rolandsson, Olov (2009) In Autoimmunity 42(6). p.507-514
Abstract
Autoantibodies against glutamic acid decarboxylase (GAD65Ab) are used in the classification of diabetes in adults. We assessed the concordance in GAD65 autoantibody levels within subjects between three different GAD65Ab radio binding assays (RBA). Plasma samples from 112 diabetes patients (median age 50 years) initially classified with type 2 diabetes was randomly selected from a local diabetes registry. Coded samples were analyzed with two RBA employing S-35-labeled GAD65. The first used the pEx9 plasmid (pEx9 RBA), the second employed the pThGAD65 plasmid (pThGAD65 RBA) to label GAD65 by in vitro transcription translation. We also used a commercial kit employing plasmid pGAD 17 labelled with 1251 (pGAD17 RBA). Subsequent analyses... (More)
Autoantibodies against glutamic acid decarboxylase (GAD65Ab) are used in the classification of diabetes in adults. We assessed the concordance in GAD65 autoantibody levels within subjects between three different GAD65Ab radio binding assays (RBA). Plasma samples from 112 diabetes patients (median age 50 years) initially classified with type 2 diabetes was randomly selected from a local diabetes registry. Coded samples were analyzed with two RBA employing S-35-labeled GAD65. The first used the pEx9 plasmid (pEx9 RBA), the second employed the pThGAD65 plasmid (pThGAD65 RBA) to label GAD65 by in vitro transcription translation. We also used a commercial kit employing plasmid pGAD 17 labelled with 1251 (pGAD17 RBA). Subsequent analyses followed standard procedures. Two different cut-offs for GAD65Ab positivity were used in all three assays. We calculated the correlation, concordance, and agreement between the assays. The proportion of GAD65Ab positivity differed between assays when low cut-offs were used (pEx9 RBA 25%, pThGAD65 RBA 17.9%, and pGAD17 RBA 12.5%, respectively). When high cut-offs were applied, the concordance between the pEx9 RBA and the pThGAD65 RBA was 97.3 while their concordance to the pGAD17 RBA was lower (88.4 and 87.4, respectively). There was a low agreement between both pEx9 RBA and pGAD17 RBA (0.45, 95% CI 0.20-0.70) and between pThGAD65 RBA and pGAD17 RBA (0.43,95% CI 0.18-0.68). We found discrepancies in determining the GAD65Ab positivity, which constitutes a problem when GAD65Ab are used clinically. Further methodological GAD65Ab assays studies are warranted. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
autoimmunity, Type 1 diabetes, type 2 diabetes, immunological technique
in
Autoimmunity
volume
42
issue
6
pages
507 - 514
publisher
Taylor & Francis
external identifiers
  • wos:000270227200005
  • scopus:70249111138
ISSN
0891-6934
DOI
10.1080/08916930902911720
language
English
LU publication?
yes
id
4360cdeb-9111-4193-9511-096aab73e607 (old id 1489816)
date added to LUP
2009-10-21 11:00:02
date last changed
2017-01-01 06:23:49
@article{4360cdeb-9111-4193-9511-096aab73e607,
  abstract     = {Autoantibodies against glutamic acid decarboxylase (GAD65Ab) are used in the classification of diabetes in adults. We assessed the concordance in GAD65 autoantibody levels within subjects between three different GAD65Ab radio binding assays (RBA). Plasma samples from 112 diabetes patients (median age 50 years) initially classified with type 2 diabetes was randomly selected from a local diabetes registry. Coded samples were analyzed with two RBA employing S-35-labeled GAD65. The first used the pEx9 plasmid (pEx9 RBA), the second employed the pThGAD65 plasmid (pThGAD65 RBA) to label GAD65 by in vitro transcription translation. We also used a commercial kit employing plasmid pGAD 17 labelled with 1251 (pGAD17 RBA). Subsequent analyses followed standard procedures. Two different cut-offs for GAD65Ab positivity were used in all three assays. We calculated the correlation, concordance, and agreement between the assays. The proportion of GAD65Ab positivity differed between assays when low cut-offs were used (pEx9 RBA 25%, pThGAD65 RBA 17.9%, and pGAD17 RBA 12.5%, respectively). When high cut-offs were applied, the concordance between the pEx9 RBA and the pThGAD65 RBA was 97.3 while their concordance to the pGAD17 RBA was lower (88.4 and 87.4, respectively). There was a low agreement between both pEx9 RBA and pGAD17 RBA (0.45, 95% CI 0.20-0.70) and between pThGAD65 RBA and pGAD17 RBA (0.43,95% CI 0.18-0.68). We found discrepancies in determining the GAD65Ab positivity, which constitutes a problem when GAD65Ab are used clinically. Further methodological GAD65Ab assays studies are warranted.},
  author       = {Daka, Bledar and Svensson, Maria K. and Lernmark, Åke and Mincheva-Nilsson, Lucia and Hallmans, Goran and Rolandsson, Olov},
  issn         = {0891-6934},
  keyword      = {autoimmunity,Type 1 diabetes,type 2 diabetes,immunological technique},
  language     = {eng},
  number       = {6},
  pages        = {507--514},
  publisher    = {Taylor & Francis},
  series       = {Autoimmunity},
  title        = {Low agreement between radio binding assays in analyzing glutamic acid decarboxylase (GAD65Ab) autoantibodies in patients classified with type 2 diabetes},
  url          = {http://dx.doi.org/10.1080/08916930902911720},
  volume       = {42},
  year         = {2009},
}