Pre-diabetes will usually be diagnosed by a doctor using either an HbA1c or a fasting plasma glucose (FPG) test. However, in some cases, an OGTT test may also be carried out.

Oral Glucose Tolerance Test (OGTT)

The OGTT is a screening test that involves testing the individual’s plasma glucose level following a glucose-rich drink (a beverage containing 75 grams of glucose).

An OGTT may be used in people that show symptoms of diabetes but have not recorded diabetic levels with the HbA1c or fasting plasma glucose tests.

The OGT test may be used for diagnosis, instead of the HbA1c in people with certain blood disorders such as shortened red blood cell life.

People who have impaired glucose tolerance (IGT) or pre-diabetes will have a plasma glucose level of less than 11.0 mmol/L (200 mg/dl) but equal to or greater than 7.8 mmol/L (140 mg/dl)

Those people who have a plasma glucose level over or equal to 11.0 mmol/l (200 mg/dl) after two hours will be asked to have a fasting plasma glucose test to confirm diabetes diagnosis.

The fasting plasma glucose test is used to diagnose diabetes, however.

Fasting Plasma Glucose Test (FGT)

The FGT test works by measuring the level of glucose in an individual’s blood after a period of fasting.

Anyone who is at a high risk of pre-diabetes should be given the FPG test. This includes those who are severely overweight or obese, people of South Asian or African-Caribbean descent, or anyone with a family history of diabetes.

The fasting plasma glucose test is performed after a person fasts for at least 8 hours.

Individuals who have a blood glucose level greater than or equal to 7.0 mmol/L (126 mg/dl) will be retested and , if the results are consistent , diagnosed with diabetes.

If the results are less than 7.0 mmol/L (126 mg/dl) but greater than 6.1 mmol/L (110 mg/dl) the individual will be diagnosed as having impaired fasting glucose, or pre-diabetes.

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