Time-Dependent Changes in Titers of GAD Antibody and Levels of Fasting Serum C-Peptide in a Patient With Slowly Progressive Type 1 Diabetes Seroconverted After the Initiation of Insulin Therapy

Abstract

We investigated the time-dependent changes in anti-GADA titers and fasting serum C-peptide (FSC) levels after GADA seroconversion in 12 patients with SPIDDM initially regarded as having type 2 diabetes at the diagnosis and became GADA-positive after the initiation of insulin therapy at our hospital between 1998 and 2015. Twelve patients were classified into 3 groups according to the time-dependent changes in the titers: 1) antibody titer ≥2000 U/mL on an enzyme-linked immunosorbent assay (ELISA) after sustained positivity on a radioimmunoassay (RIA) (n=3); 2) antibody titer 100-300 U/mL on an ELISA or ELISA conversion after sustained positivity on a radioimmunoassay (n=2); and 3) negativity on an RIA or ELISA (n=7). The FSC levels were preserved in groups 2 and 3, but exhausted (< 0.6 ng/mL) in 1.