Testing for Type 1 Diabetes


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If you suspect that you may have diabetes, you should consult your GP who will want to perform a series of tests to see how your body handles sugar, so called glucose abnormality tests.

If you start to experience any symptoms, it is likely that your doctor will want to take a blood sample to check your plasma glucose level. If this test comes back with a concentration above 11 mmol/L it is likely that you may have diabetes.

Fasting Plasma Glucose (FPG) Test

The test that is used most frequently to diagnose diabetes if you have very minor symptoms is the Fasting Plasma Glucose (FPG) test. It involves taking a sample of your blood after 8 hours without any food and measuring the concentration of glucose in the liquid part called the plasma. This is the straw coloured fluid that contains all of the ions and glucose in your blood. Different glucose concentrations indicate various problems:

  • Fasting concentrations are normal up to 5.5mmol/L ( 100mg glucose per dL)
  • A glucose concentration between 5.5-7mmol/L is classed as impaired fasting glucose. This is a risk factor for the development of type 2 diabetes.
  • A concentration of glucose above 7mmol/L is considered indicative of diabetes.

Even though the fasting plasma glucose test is used most frequently in diagnosing diabetes, sometimes the results can be wrong. In some instances, if you have a normal result in the afternoon, you may have an abnormal result in the morning. It is therefore suggested that the test be repeated to check the results are accurate, especially if the test has diagnosed you with diabetes.

Random Plasma Glucose Test


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If you experience very few of the symptoms of diabetes, the doctor may wish to do a random plasma glucose test. Like the FPG test, it is necessary to do two random tests to diagnose diabetes. Two random values above 11.1mmol/L are indicative of diabetes.

Oral Glucose Tolerance Test (OGTT)


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Another test used to help diagnose diabetes is the Oral Glucose Tolerance Test (OGTT). This test takes less time than the FPG test and is used frequently in general practice. It is often used if an FPG test has indicated that you don’t have diabetes, but you still experience many of the symptoms or have many risk factors for developing the condition.

The test involves you drinking a solution with a specified concentration of glucose within it, then having a blood sample taken two hours later. The results are as follows:

  • Glucose concentrations up to 140mg/dL are normal
  • Glucose concentrations from 140 to 199mg/dL indicate impaired glucose tolerance
  • Any glucose concentration above 200mg/dL indicates diabetes

When taking the test, approximately 2% of us will be found to have diabetes, whereas 5% will be found to have impaired glucose tolerance. Impaired glucose tolerance does not itself require further treatment, however it is a risk factor for the development of both diabetes and heart disease (cardiovascular disease).

Both the FPG and OGTT require you to have not eaten for the previous 8 hours. It is for this reason that these tests are usually done first thing in the morning.

Autoantibody Test

Sometimes, it may be necessary to do a test called the autoantibody test. The main cause of type 1 diabetes is the autoimmune destruction of the β cells of the pancreas. This test allows the doctor to check for any auto-antibodies within your blood that may be damaging your pancreas.


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