Aims/hypothesis Red blood cell distribution width (RDW) has been reported to be a risk marker of morbidity and mortality for cardiovascular disease in various study populations. However, no studies have investigated the relationship between RDW and diabetes complications. We therefore evaluated RDW as a marker of macrovascular and microvascular complications in a nationally representative sample of the adult diabetes population in the USA. Methods A cross-sectional study was performed using the nationwide 1988 to 1994 data set from the Third National Health and Nutrition Examination Survey. The association between RDW quartiles and macrovascular and microvascular complications was evaluated in 2,497 non-pregnant adults aged 20 years and older and affected by diabetes. Logistic regression modelling was used to adjust for potential confounding.

BackgroundInsulin resistance, characterized by hyperinsulinemia and normal or elevated serum glucose, is an established precursor to diabetes and cardiovascular disease. Despite fasting serum C‐peptide levels being an accurate and stable marker of endogenous insulin production used in patients with diabetes, it is unknown whether C‐peptide could serve as a marker of insulin resistance and predict outcomes in patients without diabetes.Method and ResultsThis is a retrospective cohort study using data from the NHANES‐3 (1988–1994) survey with mortality follow‐up through December 31, 2006. Participants included 5153 subjects, 40 to 74 years of age with fasting glucose ≥70 mg/dL, without diabetes by history or laboratory testing. Receiver‐operating‐curve analysis compared fasting C‐peptide against known insulin resistance measures such as fasting plasma glucose, serum insulin, HOMA‐IR, quantitative‐insulin‐sensitivity‐check‐index, and metabolic syndrome for the prediction of cardiovascular and overall death. Subjects were then stratified by quartiles of C‐peptide levels. Cox proportional‐hazards modeling compared hazards of cardiovascular and overall death amongst C‐peptide quartiles and adjusted for potential confounders of cardiovascular and diabetes risk. Fasting serum C‐peptide levels predicted cardiovascular and overall death better than other studied measures (AUC=0.62 and 0.60 respectively vs the rest, with AUC≤0.58 and ≤0.57 respectively, P<0.001). When compared with the lowest C‐peptide quartile, subjects in the highest quartile had significantly higher adjusted hazard ratios (HR) of cardiovascular death (HR=1.60, 95%CI 1.07 to 2.39) and overall mortality (HR=1.72, 95%CI 1.34 to 2.21) after controlling for confounders.ConclusionsC‐peptide levels significantly related to hazards of cardiovascular and overall death in nondiabetic adults and was a better predictor of these outcomes than serum insulin and/or glucose derived measures.