Islet Autoantibody Standardization Program 2018 Workshop: Interlaboratory Comparison of Glutamic Acid Decarboxylase Autoantibody Assay Performance

Abstract

BACKGROUND The Islet Autoantibody Standardization Program (IASP) aims to improve the performance of immunoassays measuring type 1 diabetes (T1D)-associated autoantibodies and the concordance of results among laboratories. IASP organizes international interlaboratory assay comparison studies in which blinded serum samples are distributed to participating laboratories, followed by centralized collection and analysis of results, providing participants with an unbiased comparative assessment. In this report, we describe the results of glutamic acid decarboxylase autoantibody (GADA) assays presented in the IASP 2018 workshop. METHODS In May 2018, IASP distributed to participants uniquely coded sera from 43 new-onset T1D patients, 7 multiple autoantibody-positive nondiabetic individuals, and 90 blood donors. Results were analyzed for the following metrics: sensitivity, specificity, accuracy, area under the ROC curve (ROC-AUC), partial ROC-AUC at 95% specificity (pAUC95), and concordance of qualitative and quantitative results. RESULTS Thirty-seven laboratories submitted results from a total of 48 different GADA assays adopting 9 different formats. The median ROC-AUC and pAUC95 of all assays were 0.87 [interquartile range (IQR), 0.83–0.89] and 0.036 (IQR, 0.032–0.039), respectively. Large differences in pAUC95 (range, 0.001–0.0411) were observed across assays. Of formats widely adopted, bridge ELISAs showed the best median pAUC95 (0.039; range, 0.036–0.041). CONCLUSIONS Several novel assay formats submitted to this study showed heterogeneous performance. In 2018, the majority of the best performing GADA immunoassays consisted of novel or established nonradioactive tests that proved on a par or superior to the radiobinding assay, the previous gold standard assay format for GADA measurement.

COVID-19 survival associates with the immunoglobulin response to the SARS-CoV-2 spike receptor binding domain

“…For this study, we leveraged our prior expertise (27)(28)(29)(30)(31) to develop novel LIPS liquid phase immunoassays, a format that has already been applied to the study of antibody responses to pathogens (32)(33)(34). LIPS assays have also found extensive application in autoimmunity, where they demonstrated the ability to measure with high sensitivity and specificity autoantibody responses, often varying by orders of magnitude across patients, and to detect antibody binding to conformational epitopes on antigens undergoing posttranslational modifications and with complex tertiary structures (28,31,35,36). To our knowledge, at least 3 recent reports presented data on antibodies in COVID-19 measured by LIPS in small cohorts of patients and controls using different SARS-CoV-2 antigens (37-40).…”

“…Positive and negative predictive values were calculated using the epiR R package. Assay performance in discriminating health from disease was analyzed using the area under the receiver operator characteristics curve (ROC-AUC) and the partial ROC-AUC at 95% specificity (pAUC95), to exclude diagnostically irrelevant ROC-AUC regions corresponding to very low assay specificity (36,54). The ROC-AUCs of combination of markers were calculated by performing an initial binary logistic regression for the biomarkers to be combined and then using the obtained probabilities as the test variable to build a ROC curve.…”

Sensitive detection of multiple islet autoantibodies in type 1 diabetes using small sample volumes by agglutination-PCR

“…With the solid in-house validation results, we next sought to rigorously evaluate the samplesparing ADAP assay in a blinded manner by participating in the Islet Autoantibody Standardization Program (IASP) [18]. Firstly, the IASP study featured participants from over 30 laboratories from 17 countries.…”

“…In cohort 2, the coded IASP 2018 samples were received from the IASP Committee and the University of Florida [18] to compare performance with other laboratory in a blinded fashion. This cohort included 43 new-onset T1D samples within 14 days of diagnosis (median age of 14 years, 65% male, 86% white Caucasian, disease duration < 14 days), 7 multi-autoantibody positive first degree relatives of T1D (median age of 16 years, 43% male, 100% White) and 90 matched controls (median age of 20 years, 49% male, 77% White).…”

Autoimmunity to tetraspanin-7 in type 1 diabetes

“…Radioactivity immunoprecipitated then provides an indication of autoantibody levels. The protocol provides a relatively simple and versatile means to quantify diabetes-associated antibodies and the assay format has shown good reproducibility and performance in international diabetes autoantibody standardisation workshops [ 33 – 36 ]. Unfortunately, soon after the discovery of Tspan7 as an autoantibody target it was clear that radioligand binding assays with antigen transcribed and translated in vitro were not capable of detecting diabetes-associated Tspan7 antibodies effectively [ 8 , 37 ].…”