Prevalence of Undiagnosed Diabetes in Rheumatoid Arthritis: an OGTT Study

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by an excess of cardiovascular disease (CVD) risk, estimated to be at least 50% greater when compared to the general population. Although the widespread diffusion of type 2 diabetes mellitus (T2DM) awareness, there is still a significant proportion of patients with T2DM that remain undiagnosed. Aim of this cross-sectional study was to evaluate the prevalence of undiagnosed diabetes and prediabetes in RA patients. For the present study, 100 consecutive nondiabetic RA patients were recruited. Age- and sex-matched subjects with noninflammatory diseases (osteoarthritis or fibromyalgia) were used as controls. After overnight fasting, blood samples were obtained for laboratory evaluation including serum glucose, total cholesterol, high-density lipoprotein (HDL)-cholesterol, low-density lipoprotein (LDL)-cholesterol, triglycerides, uric acid, erythrocyte sedimentation rate (ESR), high sensitivity C-reactive protein (hs-CRP), rheumatoid factor (RF), and anti-Cyclic Citrullinated Peptide Antibodies (ACPA). A standard Oral Glucose Tolerance Test (OGTT) with 75 g of glucose was performed and blood samples were collected at time 0, 30, 60, 90, and 120 minutes, for measurement of plasma glucose concentrations. The prevalence of impaired fasting glucose (IFG) (9/100 vs 12/100, P = 0.49), impaired glucose tolerance (IGT) (19/100 vs 12/100, P = 0.17), and concomitant IFG/IGT (5/100 vs 9/100, P = 0.27) was similar between groups, whereas the prevalence of diabetes was significantly higher in RA patients (10/100 vs 2/100, P = 0.02). In a logistic regression analysis, increasing age (OR = 1.13, 95% CI 1.028-1.245, P = 0.01) and disease duration (OR = 1.90, 95% CI 1.210-2.995, P = 0.005) were both associated with an increased likelihood of being classified as prediabetes (i.e. IFG and/or IGT) or T2DM. A ROC curve was built to evaluate the predictivity of disease duration on the likelihood of being diagnosed with T2DM. The area under the ROC curve was 0.67 (95% CI: 0.56-0.78, P = 0.004). We identified the best cut-off of 33 months that yielded a sensitivity of 61% and a specificity of 70% for classification of T2DM patients. According to our data, RA seems to be characterized by an elevated prevalence of undiagnosed diabetes, especially in patients with longer disease duration.