Prognostic factors for the course of beta cell function in autoimmune diabetes

This study presents a 2-yr follow-up of 281 patients, aged 15-34 yr, diagno sed with diabetes between 1992 and 1993. At diagnosis, 224 (80%) patients w ere positive for at least one of the following autoantibodies: islet cell a ntibodies (ICAs), glutamic acid decarboxylase antibodies (GADAs), or tyrosi ne phosphatase antibodies (IA-2As); the remaining 57 (20%) patients were ne gative for all three autoantibodies. At diagnosis, C-peptide levels were lo wer (0.27; 0.16-0.40 nmol/L) in autoantibody-positive patients compared wit h 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 autoim mune 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 lev el of C-peptide (odds ratio, 2.6; 95% confidence interval, 1.7-4.0) and a h igh 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 mul tivariate analysis only when initial C-peptide was not considered. Factors such as age, gender, levels of ICA or IA-2A or insulin autoantibodies (anal yzed in a subset of 180 patients) had no effect on the decrease in <beta>-c ell function. It is concluded that the absence of pancreatic islet autoantibodies at diag nosis were highly predictive for a maintained beta -cell function during th e 2 yr after diagnosis, whereas high levels of GADA indicated a course of d ecreased beta -cell function with low levels of C-peptide. In autoimmune di abetes, an initial low level of C-peptide was a strong risk factor for a de crease in beta -cell function and conversely high C-peptide levels were pro tective. Other factors such as age, gender, body mass index, levels of ICA, IA-2A or IAA had no prognostic importance.