Blood tests are done to diagnose diabetes. The following tests are done for diagnosis:
- Fasting plasma glucose (FPG)
- Oral glucose tolerance test (OGTT)
- Random plasma glucose test
Fasting plasma glucose (FPG): This test measures blood glucose level in the morning (after 8 hours of fasting) before you eat or drink anything even tea or coffee. The test can help to diagnose diabetes and pre-diabetes.
Diagnosis based on fasting plasma glucose
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- FPG <99 mg/dl is considered normal
- FPG between 100 to 125 mg/dl indicates pre-diabetes (or impaired fasting glucose)
- FPG >126 mg/dl indicates diabetes
Oral glucose tolerance test (OGTT): In this test the blood glucose level is measured in a person after drinking 75 grams of glucose solution. The test is done after at least 8 to 12 hours of fasting. The test can help to diagnose diabetes and pre-diabetes. OGTT is more sensitive as compared to FPG test for diagnosis of pre-diabetes, but it is more cumbersome as compared to FPG.
Based on the results of glucose tolerance test the following diagnoses may be made:
- Normal response: In people with normal glucose tolerance test the 2-hour glucose level remains lower than 140 mg/dl, and all values between 0 and 2 hours remain lower than 200 mg/dl.
- Impaired glucose tolerance: If your fasting plasma glucose is less than 126 mg/dl and the 2-hour glucose level is between 140 and 199 mg/dl you have impaired glucose tolerance test
- Diabetes: If your fasting plasma glucose is greater than 126 mg/dl and/or the 2-hour glucose level is greater than mg/dl repeatedly (done on different days)---you have diabetes.
- Gestational diabetes: A woman is diagnosed with gestational diabetes if she has any two of the following after 100g OGTT---fasting plasma glucose > 95 mg/dl, 1-hour glucose > 180 mg/dl, 2-hour glucose level > 155 mg/dl, or a 3-hour glucose level > 140 mg/dl.
Random plasma glucose test: The test measures blood glucose at any time of the day disregarding to when the person last ate. This test is usually done to diagnose diabetes but not pre-diabetes.
- Random blood glucose level > 200 mg/dL along with symptoms of diabetes (such as increased urination, increased thirst, unexplained weight loss) indicates that you may have diabetes.
- Your doctor may recommend FPG or OGTT to confirm the diagnosis.
If your blood sugar or blood glucose levels are elevated your doctor will recommend repeat testing on a different day to confirm the results.
Dr Poonam Sachdeva, our in-house medical expert talks about the why what and how in diabetes.
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