There are several tests used for the diagnosis of diabetes. Many such tests attempt to identify the presence of pre-diabetes, which is where blood glucose levels are higher than normal but not high enough for a diagnosis of diabetes.
The three main tests for diabetes used in the United Kingdom are as follows:
Fasting plasma glucose(FPG)test - this measures blood glucose in a person who has not eaten anything for at least 8 hours. The test can used to detect both diabetes and pre-diabetes.
Oral glucose tolerance test (OGTT)- this measures blood glucose after a person has fasted for at 8 hours, and 2 hours after he or she drinks a glucose based beverage. This test can be used to diagnose both diabetes and pre-diabetes.
Random plasma glucose test - otherwise known as a casual plasma glucose test, this measures blood glucose irrespective of when the person last ate. This test can be used to diagnose diabetes but not pre-diabetes.
If one of the aforementioned tests indicates the presence of diabetes, the individual will be given a second test on a different day. Blood glucose levels can sometimes vary quite considerably from day to day, so it's important to ensure that the initial reading wasn't simply a spike in an otherwise healthy patient.
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