The use of HbA1c in diagnosis of diabetes mellitus by WHO and ADA has come under scrutiny. Aim: To study the erythrocyte index alterations and their relationship with HbA1c for proper interpretation of HbA1c values in diabetic subjects. Materials and methods: Data from 301 diabetic patients was collected. The parameters included were fasting plasma glucose, red blood cell count, hemoglobin level, hematocrit, glycated Hemoglobin (HbA1c), MCV, MCH, MCHC and RDW. Results: A negative correlation was found between HbA1c and MCV, MCH and MCHC and positive correlation with RDW. Conclusion: Hematological parameters like MCH, MCV and MCHC should be taken into account in interpreting HbA1c levels in diagnosis and management of pre diabetes and diabetes.