Glycosylated hemoglobin is tested to know the long term monitoring of diabetes mellitus. It reflects the average blood sugar level over thepast three months. Its levels increase in poorly controlled diabetes. It can be performed at any time of the day and doesnot require any fasting conditions.Fasting blood sugar is inconvenient and also is dependent on carbohydrate rich diet hence day to day glucose variability. glycosylated hemoglobin is fast becoming an alternative to diagnose diabetes.and also as a screening test for diabetes in people highly prone to getting diabetes. In this test the hemoglobin of the patient becomes glycosylated- glucose becomes stuck to hemoglobin molecule till the lifespan of red blood cell.