Assessment of precision, concordance, specificity, and sensitivity of islet cell antibody measurement in 41 assays

Abstract

Summary. Forty-one assays were analysed at the 3rd International Workshop on the standardisation of islet cell antibodies. Analysis of precision demonstrated assays consistently detecting blind duplicates within one doubling dilution and capable of discriminating one doubling dilution differences in islet cell antibody concentration. Some assays, however, reported duplicates discrepantly by more than seven doubling dilutions, and consequently could not distinguish even large quantities of islet cell antibodies. Precision was best in assays from laboratories which had participated in all three Standardisation Workshops and was not dependent upon methodology. The use of the Juvenile, Diabetes Foundation reference islet cell antibody standard and standard curves reduced the scatter of results, and was best amongst assays with better precision. Twenty-seven assays reported all ten blood donor sera as negative. However, 14 assays did not, and specificity (negativity in health) was < 50% in three assays. Low specificity was strongly associated with poor precision. The detection limit of assays ranged from < 5 to 50 JDF units and was partially dependent upon methodology. Assays incorporating extended incubation had the lowest detection limits without a decrease in the specificity of the ten blood donor sera. Precise quantification is fundamental for the standardisation and comparability of islet cell antibodies. Precise quantitative assays have been identified and reference standards and common units established. [7,8], or undergoing therapeutic trials with cyclosporine [9,10]. Since ICA were first described [11], numerous methodological modifications to the standard indirect immunofluorescent (IFL) assay have been proposed [12][13][14][15][16][17][18]. An assessment of inter-assay comparability was essential for the validity of ICA in diabetes research, and accordingly, four International Workshops have been held. The first showed a large scatter of results between laboratories, and suggested that the availability of reference sera would allow laboratories to express ICA in arbitrary, but common units [19]. A reference standard -Juvenile Diabetes Foundation (JDF) standard -was proposed and tested in the stage II Workshop. The use of standard curves constructed from this standard improved precision and concordance between laboratories [20,21].The stage III workshop was designed so as to (1) assess the precision, and (2) begin studies on the specificity (negativity in health), and sensitivity (positivity in disease) of the ICA assays. These parameters in 41 assays are analysed here, and their importance in the development of an international standardisation programme of ICA measurement discussed.

Adrenal and ovarian autoimmunity

“…To avoid discrepancies in adrenal autoantibodies measurements, an international standardization and proficiency program should be performed in the near future, similar to that successfully performed for isletcell autoantibodies (72)(73)(74).…”

Diabetes Antibody Standardization Program: evaluation of assays for autoantibodies to glutamic acid decarboxylase and islet antigen-2

“…The Diabetes Autoantibody Standardization Program (DASP), a collaboration of the Immunology of Diabetes Society (IDS) and the US Centers for Disease Control and Prevention, was established on the basis of a series of IDS workshops to improve and standardise the measurement of the autoantibodies predictive of type 1 diabetes [5][6][7][8]. The major goals of DASP are to assist laboratories in improving methods by providing technical support, training and information, to organise workshops for harmonisation of antibody testing among laboratories, and to provide reference materials for the development of new measurement technologies.…”

Diabetes Antibody Standardization Program: First Assay Proficiency Evaluation

“…This issue has been addressed in a series of international workshops and antibody standardization and proficiency programs since the first islet cell antibody (ICA) standardization workshop in 1985 (6,7). Subsequent workshops examined other islet autoantibodies as they were described, and the combined islet autoantibody workshop in 1995 included antibodies to GAD, protein tyrosine phosphatase IA-2, and insulin, as well as ICA.…”

“…(8). The major achievements of these activities have been the introduction of a reference standard preparation and units for ICA measurement, validation of diabetes-associated antibody markers and methods for their measurement, and an improved concordance between laboratory measurements (6,8). The ICA reference standard has recently been given World Health Organization (WHO) status and undergone preliminary evaluation in a small number of laboratories as a reference reagent for autoantibodies to GAD and IA-2 (9).…”