Fasting blood glucose may go up to 140 mg/dl for just once or twice due to factors such as what you ate the previous day as well as stress, drinking coffee etc. It is essential to consult an internal medicine specialist to consult for higher values. For the results around 140 mg /dl, postprandial blood sugar may be studied in the laboratory after 2 hours following the meal. If the result of this test is around 140-160 mg/dl, Oral Glucose Tolerance Test is performed. You are made to drink 75 or 100 g glucose, depending on your weight, after taking the fasting blood. This is followed by taking your blood for 4 times at ½ or 1-hour intervals. Glucose is studied from these blood samples. Insulin hormone discharge against the standard glucose given to you and cleaning your blood glucose from blood samples in this period is checked by means of a tolerance curve. If the results obtained are considered high by the expert in the laboratory, you should consult to an endocrinologist.