This test is done for assessing / diagnosing Diabetes and evaluating long term control of blood glucose concentrations in diabetic patients. It reflects the mean glucose concentration over the previous period of 3 months and it is a good indicator of long term glycemic control it should be done with blood and urine glucose measurements for better clinical understanding.The hemoglobin A1c test may be used to screen for and diagnose diabetes and prediabetes in adults. Hemoglobin A1c, also glycated hemoglobin or A1c, is formed in the blood when glucose attaches to hemoglobin. The higher the level of glucose in the blood, the more glycated hemoglobin is formed. In short it tells the sugar of three months.