How is diabetes diagnosed?

Diabetes is diagnosed by a blood test. Most people with type 1 diabetes and many with type 2 diabetes will present with symptoms of diabetes such as: increased thirst, urination and tiredness. Some people will also have signs of slow healing of wounds or persistent infections. However many people with type 2 diabetes have no symptoms at all.

The blood test is taken from a vein and sent to a pathology lab. The test may be either a fasting 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 are present and fasting blood test result is at or above 7.0mmol/L or a random blood test result is at or above 11.1mmol/L
  • HbA1c blood test result is ≥ 6.5% (48 mmol/mol)
  • There have been no symptoms and two abnormal blood glucose tests (as above) on separate days.


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

A diagnosis of diabetes should not be made only by using a blood glucose meter and finger prick, or by 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 pathology to confirm the diagnosis.

How will my doctor know which 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 confirm with further blood tests if type 1 diabetes is suspected.

Your doctor may also check for ketones in your blood or urine which can help with the diagnosis. Ketones can be a sign that you lack insulin (and is usually associated with rapid weight loss). There are other tests which can help to determine the type of diabetes, such as insulin levels and certain antibodies in the blood, but these can take several weeks to confirm. In the meantime, it is important that you keep in contact with your doctor and monitor your blood glucose levels. If you are unwell your doctor may refer you to a hospital or specialist immediately for treatment.

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 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 is a condition in which blood glucose levels are higher than normal but not high enough to be diagnosed as type 2 diabetes.

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

  • In the three days leading up to the test you should eat and drink adequate carbohydrate (starchy foods), greater than 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 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)
  • No diabetes.


References: “Diabetes Management in General Practice”. 2012/13, RACGP & Diabetes Australia.