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Combinatorial Islet Autoantibody Workshop

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#1. Title:

  • The 1st Combined Autoantibody workshop was sponsored by a special grant from the Juvenile Diabetes Foundation and organized by the Barbara Davis Center for Childhood Diabetes in Denver. A full report has been submitted for publication.
  • The aim of the workshop was to evaluate the ability of individual autoantibody assays to distinguish between disease and non-disease, and for the first time to assess the use of assays in combination

#2. Sera & Assays:

  • Coded aliquots of sera on 51 patients with new onset type I diabetes (all sampled within 7 days of diagnosis) and on 101 healthy controls with no family history of diabetes were distributed to participating laboratories.
  • The diabetic patients ranged in age up to 45 years and all had the initial clinical diagnosis of type I diabetes. However, in the final analysis, diabetic sera were restricted to 43 subjects aged under 30 years, because most of the sera from patients aged over 30 were antibody negative.

#3. Specificity vs Sensitivity:

  • The laboratories used their previously established in-house cut-offs to score each serum as positive or negative. Using the in-house cut-offs, this is a plot for each assay of specificity versus sensitivity. In this workshop sensitivity is the percentage of diabetic sera that were positive in a given assay, and specificity is the percentage of control sera that were negative.
  • The figure shows that a number of assays of different types detect 10% or more of controls as positive, using in-house cut-offs. Increasing the cut-off for a given assay improves the specificity (and at the same time lowers sensitivity). Both sensitivity and specificity need to be accounted for when comparing assays. Therefore a new workshop cut-off was calculated for each assay, based on the 99th percentile of levels in the controls. The new cut-offs were then applied to the diabetic sera to determine "adjusted sensitivity". In this way sensitivity of the assays could be compared, with specificity held constant at 99%.

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