Diagnosis

How diabetes is diagnosed

Most people with type 1 diabetes and many with type 2 diabetes will present with symptoms of diabetes. However some people with type 2 diabetes may have no symptoms at all.

Diabetes is diagnosed by a blood test.  The plasma blood test is taken from a vein and sent to a pathology lab. The test may be either a fasting blood test (no food or fluid except water for eight hours, e.g. overnight) or a random test taken anytime during the day, or an Oral Glucose Tolerance Test (OGTT).

Diabetes is diagnosed when:

• Symptoms of diabetes are present and a random (non fasting) blood glucose level is greater than 11mmol/L
• A fasting plasma glucose is greater than 7mmol/L
• 2 hour plasma glucose is greater than 11 mmol/L during an oral glucose test.

Can diabetes be diagnosed with a blood glucose metre or urine test?

A diagnosis of diabetes should not be made only by using a blood glucose metre and finger prick, or by a urine glucose test. Although, your Doctor may take a blood test with a finger prick in the consulting room, you will still need a further blood test sent to a pathology laboratory to confirm the diagnosis.

Oral Glucose Tolerance Test

What is an OGTT (oral glucose tolerance test)?

An OGTT involves a blood test taken from a vein, usually the arm, at a pathology lab.

What you need to do before a OGTT test

• Three days before you should eat and drink adequate carbohydrate (starchy foods), about 150gms per day
• You will need to fast for eight hours before the test, this is usually done overnight
• A fasting blood glucose test is taken. You are then given a sweet drink that contains 75g of glucose
• Your blood glucose level is checked at one hour and again at two hours after the glucose drink

From this you will be given a diagnosis of either:

• Diabetes
• Pre diabetes - impaired fasting glucose (IFG) or impaired glucose tolerance (IGT)
• Nothing diagnosed.

References: “Diabetes Management in General Practice”. 2009/10, RACGP & Diabetes Australia.

How the doctor will determine what type of diabetes it is?

As an adult, it can sometimes be difficult to distinguish between type 1 diabetes and type 2 diabetes. Your Doctor will have to go on the history and severity of the symptoms, then can confirm with further blood tests if type 1 diabetes is suspected.

What if my blood test is not normal, but not diabetes either?

Some people will have a fasting blood level that is above the normal range, but not high enough to be diagnosed as diabetes. For example, a fasting blood glucose level that is between 5.5mmol/L and 6.9mmol/L is above the normal range but does not confirm or rule out diabetes or pre-diabetes. In this situation your doctor should order an oral glucose tolerance test (OGTT).

Pre-diabetes

Pre-diabetes is a condition in which blood glucose levels are higher than normal but not high enough to be diagnosed as type 2 diabetes.  It may develop into type 2 diabetes in 5 – 10 years if not managed.