Abstract: HbA_1c is formed over a period of two to three months and reflects the glycaemic status of a patient over the past two to three months for this reasons HbA1C test has been used for diabetics followup and diagnosis. The relationship between HbA_1c and average blood glucose is complex but has been studied by the Diabetes Control and Complications Trial (DCCT). A new internationally standardized method for reporting HbA_1C has been developed by the International Federation of Clinical Chemistry (IFCC). This will report HbA_1C in mmol per mol of hemoglobin without glucose attached. HbA_1c has now been recommended by an International Committee and by the ADA (American Diabetes Association) as a mean to diagnose diabetes and as a screening test for persons at high risk of diabetes. Also, the International Diabetes Federation and American College of Endocrinology (ACE) recommend HbA_1c values below 48 mmol moL^–1 (6.5%). The 2010 American Diabetes Association Standards of Medical Care in Diabetes added the A1c 48 mmol moL^–1 (6.5%) as another criterion for the diagnosis of diabetes mellitus.