Red Cell Distribution Width as an Emerging Biomarker of Glycemic Control and Metabolic Dysregulation in Type 2 Diabetes Mellitus

Abstract

Type 2 diabetes mellitus (T2DM) remains a global health burden characterized by chronic hyperglycaemia and progressive micro‑ and macrovascular complications. Glycated haemoglobin (HbA1c) and fasting plasma glucose are widely used to assess long‑term glycaemic control, yet they require laboratory infrastructure and can be influenced by factors such as haemoglobinopathies and anaemia. Red cell distribution width (RDW) reflects the variability of erythrocyte sizes; its routine availability in complete blood counts makes it a candidate biomarker for metabolic stress and inflammation. Recent epidemiological and mechanistic studies suggest that increased RDW correlates with poor glycaemic control, chronic inflammation, and diabetic complications. The present narrative review synthesises mechanistic links between T2DM and RDW, summarises observational and longitudinal studies exploring the association between RDW and glycaemic indices, discusses RDW as a predictor of micro‑ and macrovascular complications, and highlights clinical utility, limitations and future research directions. Evidence from at least 30 unique studies indicates that elevated RDW is associated with higher HbA1c, triglycerides and LDL cholesterol, increased risk of diabetic nephropathy and cardiovascular mortality, and may reflect inflammation‑mediated erythrocyte dysfunction. Despite heterogeneity among studies, RDW emerges as a cost‑effective, readily available adjunct marker that, combined with conventional glycaemic indices, could enhance risk stratification in T2DM.