Abstract
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A Comparison of Serum and EDTA Plasma in the Measurement of Glutamic Acid Decarboxylase Autoantibodies (GADA) and Autoantibodies to Islet Antigen-2 (IA-2A) Using the RSR Radioimmunoassay (RIA) and Enzyme Linked Immunosorbent Assay (ELISA) Kits
by Kobra Rahmati, Åke Lernmark, Charlotte Becker, Anna Foltyn-Zadura, Karin Larsson, Sten-Anders Ivarsson, Carina Törn
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Background: Glutamic acid decarboxylase antibodies (GADA) and tyrosine phosphatase antibodies (islet antigen-2 antibodies; IA-2A) are used in clinical practise to identify type 1 diabetes.
Methods: GADA and IA-2A were measured with RSR-ELISA kits in samples from 76 newly diagnosed type 1 diabetic children and 120 healthy controls. The aim was to evaluate performance of RSR-ELISA kits for GADA and IA-2A when serum and Ca2+ treated plasma were used.
Results: GADA achieved high area under the curve (AUC) both for serum 0.95 (95%CI 0.90-0.99) and for Ca2+ treated plasma 0.95 (95%CI 0.91-0.99). At specificity 98%, sensitivity was 84% for serum and 87% for Ca2+ treated plasma. IA-2A achieved AUC 0.92 (95%CI 0.87-0.97) for serum and 0.94 (95%CI 0.90-0.98) for Ca2+ treated plasma. Using the lowest standard (15 WHO-Units/ml) as cut-off, specificity for serum was 100% and for Ca2+ treated plasma 99% with sensitivity 74% in both cases. Sensitivity was higher in ELISA compared to RIA (74%; p=0.0080) for GADA measurement and similar for ELISA and RIA IA-2A measurements (76%; p=0.50).
Conclusion: Both RSR-ELISAs, GADA and IA-2A showed excellent performance for serum as well as for Ca2+ treated plasma.
DOI: Clin. Lab. 2008;54:227-235
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