Usually diabetes is diagnosed using either the “fasting plasma glucose” test or the ”random plasma glucose” test. In the “fasting plasma glucose” test the patient may not eat anything over night and then must get a blood sample from a vein in the inner part of the arm. Then, the amount of glucose is measured and for a child a normal level is under 130 mg/dL. For an adult under 115 mg/dL is normal. For the ”random plasma glucose” a blood sample is taken and the amount of glucose is measured. If the patient has a high blood sugar level over 200 mg/dL then they have diabetes.
Sometimes, although it is very rare, an oral glucose tolerance test (OGTT) is taken. The patient must fast over night and the following morning a blood sample is taken. Then, the patient drinks a very sugary drink and has their blood re-taken over several hours. While the sugar breaks down the blood sugar level should rise very quickly and then lower very quickly. If the patient is diabetic then the blood sugar rises higher than normal very quickly and lowers very slowly. So, after 2 hrs a blood test is taken and if the blood sugar level is 200 mg/dL then the patient is diabetic.