Serum Complement C3 and Type 2 Diabetes in Rheumatoid Arthritis: A Case-control Study

Background: Recent evidence demonstrated a potential role of complement C3 as a candidate biomarker of cardiometabolic risk in the general population. Objective: Aim of the present study was to investigate the correlation between complement C3 levels and comorbid Type 2 Diabetes (T2DM) in Rheumatoid Arthritis (RA) patients. Methods: For the present study, 40 consecutive diabetic RA patients (RA/T2DM+ group) and 80 consecutive RA patients without diabetes (RA/T2DM- group) were recruited. Results: Patients in the RA/T2DM+ group were significantly older (p < 0.0001), had a longer RA duration (p < 0.0001) and higher disease activity (p = 0.006) compared to controls. Moreover, patients in the RA/T2DM+ group had significantly higher levels of ESR (p < 0.0001), CRP (p < 0.0001) and complement C3 (p < 0.0001). A logistic regression model was built to ascertain the effect of selected variables (age, RA duration, BMI, ESR, C3, lnCRP, corticosteroid use) on the likelihood that patients have T2DM. Longer RA duration, ESR and C3 were associated with an increased likelihood of being classified as T2DM. Finally, we built ROC curves to evaluate the predictivity of RA duration, complement C3 and the combination of both variables on the likelihood of being diagnosed with T2DM. The area under the ROC curve was 0.79 (p < 0.0001) for RA duration, 0.71 (p < 0.0001) for complement C3 and 0.89 (p < 0.0001) for the combination of both variables. Conclusion: According to our data complement C3 levels can predict the presence of T2DM in RA patients.