Prognostic Factors for the Course of β Cell Function in Autoimmune Diabetes1

This study presents a 2-yr follow-up of 281 patients, aged 15–34 yr, diagnosed with diabetes between 1992 and 1993. At diagnosis, 224 (80%) patients were positive for at least one of the following autoantibodies: islet cell antibodies (ICAs), glutamic acid decarboxylase antibodies (GADAs), or tyrosine phosphatase antibodies (IA-2As); the remaining 57 (20%) patients were negative for all three autoantibodies. At diagnosis, C-peptide levels were lower (0.27; 0.16–0.40 nmol/L) in autoantibody-positive patients compared with autoantibody-negative patients (0.51; 0.28–0.78 nmol/L; P < 0.001). After 2 yr, C-peptide levels had decreased significantly in patients with autoimmune diabetes (0.20; 0.10–0.37 nmol/L; P = 0.0018), but not in autoantibody-negative patients. In patients with autoimmune diabetes, a low initial level of C-peptide (odds ratio, 2.6; 95% confidence interval, 1.7–4.0) and a high level of GADAs (odds ratio, 2.5; 95% confidence interval, 1.1–5.7) were risk factors for a C-peptide level below the reference level of 0.25 nmol/L 2 yr after diagnosis. Body mass index had a significant effect in the multivariate analysis only when initial C-peptide was not considered. Factors such as age, gender, levels of ICA or IA-2A or insulin autoantibodies (analyzed in a subset of 180 patients) had no effect on the decrease in β-cell function. It is concluded that the absence of pancreatic islet autoantibodies at diagnosis were highly predictive for a maintained β-cell function during the 2 yr after diagnosis, whereas high levels of GADA indicated a course of decreased β-cell function with low levels of C-peptide. In autoimmune diabetes, an initial low level of C-peptide was a strong risk factor for a decrease in β-cell function and conversely high C-peptide levels were protective. Other factors such as age, gender, body mass index, levels of ICA, IA-2A or IAA had no prognostic importance.