Your body uses blood glucose, sometimes known as sugar, as its primary energy source. It originates in the food you eat and is transported to every cell in the body via the blood to be used for a variety of purposes. Blood sugar levels rising indicate the presence of diabetes, either Type 1 or Type 2, or prediabetes. Diabetes is defined as a value of 126 mg/dL while fasting or higher than 200 mg/dL following two hours of eating or consuming a glucose drink. Your readings are regarded as prediabetic if they fall within the range of 100 to 125 mg/dL. If you have prediabetes, are over 35 years old, have a body mass index greater than 25, or are a pregnant woman with diabetes, you should test your blood glucose levels on a regular basis. This test is useful to monitor the effect of diabetes medications; identify blood sugar levels that are high or low; track your progress in reaching your overall treatment goals; learn how diet and exercise affect blood sugar levels; understand how other factors, such as illness or stress affect blood sugar levels. This test includes a fasting sample, then the patient is given 75 g of glucose drink and second sample is taken exactly after 2 hours. You cannot eat or drink till both the samples have been taken.