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Which is the most reliable diagnostic test for diabetes?

Q: Which test is more reliable among oral glucose tolerance test (OGTT) and routine blood glucose test to diagnose diabetes? I am a 46 years old woman having glucose levels of 98 mg/dl fasting and 140 mg/dl 2 hours after having a normal breakfast, in the routine blood glucose test. However, in the OGTT test, plasma glucose was 97 mg/dl fasting and 260 mg/dl 2 hours after having 100 g glucose water. What do these results indicate? Why is there a variation?

A:The best way to test diabetes is by checking fasting glucose and 2 hours after taking 75 gram glucose, especially in a thin person. In obese middle aged individuals, fasting may be enough.

  • Normal - Fasting plasma glucose (FPG) <100 mg/dL
  • Two-hour glucose during OGTT <140 mg/dl (7.8 mmol/L).
  • Pre diabetes (IFG and IGT)
  • Impaired fasting glucose (IFG) - Fasting plasma glucose between 100 mg/dL and 125 mg/dL
  • Impaired glucose tolerance (IGT) - Two-hour plasma glucose value during a 75 gram oral glucose tolerance test between 140 and 199 mg/dl
  • Diabetes mellitus - FPG at or above 126 mg/dL, a two-hour value in an OGTT (2-h PG) at or above 200 mg/dL (11.1 mmol/L), or
  • A random (or casual) plasma glucose concentration = 200 mg/dL in the presence of symptoms. The diagnosis of diabetes must be confirmed on a subsequent day by measuring any one of the three criteria.
Most likely you have diabetes based on the test but it's worth repeating it again with 75 gm of glucose.


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