If you experience symptoms of severe increased thirst, frequent urination, unexplained weight loss, increased hunger, tingling of your hands or feet -- your doctor may suspect diabetes. To confirm the diagnosis, a fasting plasma glucose test or a casual plasma glucose test will be performed.
The fasting plasma glucose test (FPG) is the preferred method of diagnosing diabetes because it is easy to do, convenient and less expensive than other tests, according to the American Diabetes Association.
How Do I Prepare for the Test?
You will not be allowed to eat anything for 10-12 hours before the FPG test.
Blood will be drawn and sent to the lab for analysis.
Normal fasting blood glucose is between 70 and 100 milligrams per deciliter or mg/dL for people who do not have diabetes. The standard diagnosis of diabetes is made when two separate blood tests show that your fasting blood glucose level is greater than or equal to 126 mg/dL.
However, if you have normal fasting blood glucose, but you have risk factors for diabetes or symptoms of diabetes and your fasting blood glucose is normal, your doctor may decide to do a glucose tolerance test (see below) to be sure that you do not have diabetes.
Some people have a normal fasting blood glucose reading, but their blood glucose rapidly rises as they eat. These people may have glucose intolerance. If their blood glucose levels are high enough, they may be diagnosed with diabetes.
The casual plasma glucose test is another method of diagnosing diabetes. During the test, blood glucose is tested without regard to the time since the person's last meal. You are not required to abstain from eating prior to the test.
A glucose level greater than 200 mg/dL may indicate diabetes, especially if the test is repeated at a later time and shows similar results.
The oral glucose tolerance test is yet another method used to detect diabetes, but it is usually only done during pregnancy to diagnose gestational diabetes or for someone who is suspected of having type 2 diabetes yet has a normal fasting glucose level. It can also be performed to diagnose pre-diabetes.
Diabetes can cause major health problems if you do not keep your blood glucose in check. However, you can stay healthy and feel good despite your diagnosis if you follow your doctor's recommended treatment plan and maintain a healthy lifestyle. By choosing foods wisely, exercising regularly, maintaining a normal weight, reducing your stress level and making other modest lifestyle changes, living with diabetes will be easier.
Reviewed by Certified Diabetes Educators in the Department of Patient Education and Health Information and by physicians in the Department of Endocrinology at The Cleveland Clinic.
Edited by Brunilda Nazario, MD, WebMD, October 2004.
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