Association Between Red Cell Distribution Width and Glycated Hemoglobin in Type 2 Diabetes Mellitus: A Case-Control Study

Background: Type 2 diabetes mellitus (T2DM) is a global public health concern, particularly prevalent in low- and middle-income countries like India. Glycated hemoglobin (HbA1c) is the gold-standard marker for assessing long-term glycemic control. Red cell distribution width (RDW), an index routinely reported in complete blood count, has recently gained interest for its potential association with diabetes-related complications. This study aimed to evaluate the association between RDW and HbA1c levels in patients with T2DM and assess whether RDW could serve as a supplementary marker for glycemic status. Methods: A hospital-based analytical case-control study was conducted in the Department of Pathology at a tertiary care teaching hospital over a two-month period from June to July 2021. A total of 200 participants were included, comprising 150 patients with confirmed T2DM and 50 nondiabetic controls. All hematological and biochemical measurements were obtained from blood samples collected at a single time point during the study period. Eligible participants were recruited using consecutive sampling during the study period. Diagnosis of T2DM was based on the American Diabetes Association diagnostic criteria. Participants with anemia, hematologic disorders, malignancies, chronic liver or kidney disease, pregnancy, or acute infections were excluded to minimize confounding influences on hematological parameters. Continuous variables were expressed as mean ± standard deviation. Intergroup comparisons were performed using Student’s t-test, and Pearson’s correlation analysis was used to evaluate the association between HbA1c and RDW. Statistical significance was defined as p < 0.05. Results: A total of 200 participants were analyzed, with a mean age of 58.27 ± 10.43 years. The diabetic cohort demonstrated significantly higher HbA1c levels (8.84% ± 2.33%) than nondiabetic controls (6.37% ± 1.82%, p < 0.001). However, mean RDW values were comparable between the two groups (13.59% ± 1.31% in diabetics vs. 13.64% ± 2.13% in controls; p = 0.808). Within the diabetic group, a statistically significant but weak positive correlation was observed between HbA1c and RDW (r = 0.126, p = 0.024), suggesting that increased variability in red blood cell size may be associated with poorer glycemic control. Additionally, a modest negative correlation between HbA1c and age was identified (r = -0.205, p = 0.012). No significant association between RDW and HbA1c was observed in the nondiabetic control group. Conclusion: The findings suggest a modest but significant association between RDW and HbA1c in individuals with T2DM. Given its cost-effectiveness and availability, RDW may serve as an adjunct marker in diabetes monitoring, particularly in resource-constrained settings. Further large-scale studies are warranted to validate its clinical utility.