Doctors often suspect diabetes when one or more symptoms are experienced by a patient. Before they actually diagnose a person with diabetes, however, diabetes diagnosis tests will be performed. These could consist of a fasting plasma glucose test, a casual plasma glucose test or a glucose tolerance test.

Fasting Plasma Glucose Diabetes Test (FPG):
Measures the blood glucose level after not eating for ten to twelve hours. Fasting blood glucose for a person without diabetes is 70 to 115 mg/dL. If two separate tests show a level equal to or greater than 126 m/dL, a diagnosis of dibetes is made. (A normal reading would be between 70 and 115 mg/dL.) Easily administered, less costly, and convenient for the patient, this test is the preferred method of diagnosing diabetes according to the American Diabetes Association.

Casual Plasma Glucose Diabetes Test:
Blood glucose is tested without regard to when the last meal was eaten. Glucose levels greater than 200mg/dL may indicate diabetes, particularly if similar results are obtained from later tests.

Glucose Tolerance Test (GTT):
This is a test used to measure the body’s ability to metabolize glucose. It is another method used to detect diabetes, but is normally only performed during pregnancy. Other reasons for this type of diabetes test include testing when diabetes is suspected even though there is a normal fasting glucose, or in diabetes research studies. There are two types of glucose tolerance tests.

Oral Glucose Tolerance Test (OGTT)

This is the most common glucose tolerance test. A person must fast overnight before taking this test. Blood and urine samples are taken, and then the person drinks a solution with a specific amount of glucose. Every hour for three hours, blood will be taken again and the blood glucose levels will be measured. Levels above normal can diagnose Type II or gestational diabetes.

Intravenous Glucose Tolerance Test (IGTT)

This glucose tolerance test is not common. A person’s blood glucose is measured, and then he is given a specific amount of glucose intravenously (directly into the vein) for three minutes. During this, his glucose is measured after the first minute, and then again at the end of the three minute injection. Low levels (below normal) indicate Type 1 diabetes in some people.

There are some people that have a normal fasting blood glucose reading, but as they eat, their glocose levels rise rapidly. This may be caused by glucose intolerance. If the glucose levels are very high, they may be diagnosed as diabetic.

A Note About Impaired Fasting Glucose Diabetes Test
This is a new diagnostic category. Some people have fasting glucose values of 110-125 mg/dL. This is higher than normal but less than a diabetic. It is estimated that 13.4 million people have impared fasting glucose. It is not yet known how to predict which will develop diabetes, or its prevention, but scientists are working on it.