Islet cell antibody frequency differs from that of glutamic acid decarboxylase antibodies/IA2 antibodies after diagnosis of diabetes

Abstract

The combination of glutamic acid decarboxylase (GAD) 65 antibodies (GADA) and protein tyrosine phosphatase‐like protein IA2 antibodies (IA2‐ab), measured by radioligand binding assays, has been suggested to replace islet cell antibodies (ICA), measured by indirect immunofluorescence, as a marker for autoimmune type 1 diabetes. The aim of this study was to compare the frequency of ICA and GADA and/or IA2‐ab not only at, but also after the diagnosis of diabetes. ICA, GADA and IA2‐ab were therefore assessed at and up to 11 y after the diagnosis of diabetes in 86 children (1‐15‐y‐old). At diagnosis, ICA were found in 74 (86%) and GADA and/or IA2‐ab in 79 (92%) of the diabetic children. Hence, there was no major difference in frequency between ICA and GADA and/or IA2‐ab at diagnosis of diabetes. At follow‐up, however, ICA were less frequent than GADA and/or IA2‐ab; 1–3 y after diagnosis ICA were found in 12 (44%) and GADA and/or IA2‐ab in 24 (89%) of 27 children (p = 0.001); 4–6 y after diagnosis ICA were found in 7 (24%) and GADA and/or IA2‐ab in 27 (93%) of 29 children (p < 0.0001); 7–11 y after diagnosis ICA were found in 4 (13%) and GADA and/or IA2‐ab in 21 (70%) of 30 children (p < 0.0001). We conclude that the frequency of ICA does not always correspond to that of GADA and/or IA2‐ab. Many years after diagnosis of diabetes, measurements of GADA and IA2‐ab, but not ICA, detect autoimmunity in high frequency.