How is the OGTT carried out?
The test is performed at TML Pathology collection centres and involves drinking a glucose solution at the collection centre and having blood taken at set times. It is important to contact the collection centre prior to your test to be given detailed instructions on how to prepare for it.Following these instructions will help avoid a false result.The test will take approximately 2.5 hours (half an hour rest prior to test and two hours test time).
What do the results mean?
Results of the OGTT not only diagnose diabetes mellitus(referred to as diabetes) but can determine if you have impaired fasting glucose (IFG) or impaired glucose tolerance (IGT). Having either of these conditions indicates a significantly increased risk of developing diabetes in future.IFG is diagnosed when your fasting glucose level is6.1 - 6.9 mmol/L and the 2 hour blood test results after your glucose drink is less than 7.8 mmol/L.IGT is diagnosed when your fasting blood glucose level is less than 7.0 mmol/L and your 2 hour result after your glucose drink is 7.8 - 11.0 mmol/L.
Diabetes is diagnosed when you have shown an elevated blood glucose result on two separate occasions. This could be a fasting blood glucose result ≥7mmol/L or the2hr blood glucose result ≥11.1 mmol/L or an HbA1c result≥6.5% (which can also be reported as ≥48mmol/L).
How often should I have an OGTT?
Anyone at high risk of developing type 2 diabetes should be checked for diabetes. If you are diagnosed with either IFG or IGT it is important to have the glucose tolerance test repeated at 12 months initially, then as indicated by the results.
Allergies
As part of this test you are required to drink a glucose solution which contains the following food additives:
- 330 - ascorbic acid
- 211 - sodium benzoate
- 202 - potassium sorbate
- Sulphites
Do not proceed with the test if you have a known allergy to any of these. Contact your doctor and advise your allergy will prevent you from proceeding with the OGTT drink.
Are there fees involved?
Medicare will provide a rebate for the test providing all criteria and guidelines are met.
Use of the OGTT in pregnancy
Some women will develop diabetes in pregnancy(gestational diabetes).It is recommended that women are screened for gestational diabetes when they are between 24 and 28 weeks pregnant by having a 2 hour 75g OGTT.
Women who have had diabetes in pregnancy are at risk of developing type 2 diabetes in the future and should have a follow-up OGTT 6-8 weeks after the birth of their baby, then regular follow-up as indicated by the results of this test.
