Diabetes mellitus is diagnosed based on a high level of glucose (sugar) in the blood. Blood sugar test, done fasting and 2 hours after breakfast, is used for the diagnosis of diabetes.
How is the test done?
Fasting blood glucose: In this test, a person is asked to fast overnight, at least 8 hours, and the level of glucose in the blood is then checked. Post prandial (PP) blood glucose: This is tested two hours after having a meal. It serves as a challenge for the body to regulate the blood sugar after a meal. Random blood sugar or glucose test is that which is done at any other time. The blood glucose can also be tested after giving 75 gm glucose by mouth (glucose challenge test). This is useful for detecting borderline diabetes and a condition called "impaired glucose tolerance". Blood glucose tests are also needed for checking the control in diabetes.
What are the normal values?
Normal fasting plasma glucose levels are less than 110 mg/dl. Normal PP plasma glucose levels are less than 140 mg/dl.
What are the abnormal values?
A fasting plasma glucose level of more than 126 mg/dl indicates diabetes mellitus. A level between 110-125 mg/ dl is called "impaired fasting glucose". A PP or random plasma glucose level of more than 200 mg/dl indicates diabetes mellitus. A level between 140-199 mg/ dl is called "impaired glucose tolerance". A blood sugar exceeding the level of 200 mg/dl or higher generally indicates the presence of diabetes.
What is the role of insulin?
The body breaks down food into glucose (sugar) and uses it as a source of energy. Insulin helps the cells of the body to utilize this glucose for energy, and to store the excess in the liver for later use. Thus insulin regulates the blood glucose (sugar) levels. In diabetics, the body does not produce enough insulin or does not use the produced insulin effectively. This results in a high level of glucose in the blood ("hyperglycemia").