For diagnosis of diabetes mellitus, fasting blood glucose level should be more than:
**Core Concept**
Diabetes mellitus is a metabolic disorder characterized by hyperglycemia due to insulin deficiency or resistance. The diagnosis of diabetes mellitus involves measuring the fasting blood glucose (FBG) level, which is a critical parameter for assessing glucose homeostasis.
**Why the Correct Answer is Right**
The American Diabetes Association (ADA) recommends a fasting blood glucose level of 126 mg/dL or higher for the diagnosis of diabetes mellitus. This threshold is based on the fact that a fasting glucose level above this value indicates impaired glucose tolerance and insulin deficiency, which are hallmarks of diabetes mellitus. The mechanism underlying this threshold involves the impaired glucose uptake by peripheral tissues, leading to hyperglycemia.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a fasting blood glucose level below 100 mg/dL is considered normal, and levels between 100-125 mg/dL are indicative of impaired fasting glucose (IFG).
**Option B:** This option is incorrect because a fasting blood glucose level of 120 mg/dL is still within the normal range, and levels above 126 mg/dL are required for a diagnosis of diabetes mellitus.
**Option D:** This option is incorrect because a fasting blood glucose level of 140 mg/dL is indicative of impaired glucose tolerance (IGT), but not diabetes mellitus.
**Clinical Pearl / High-Yield Fact**
Remember that the ADA recommends a repeat test on a different day to confirm the diagnosis of diabetes mellitus if the initial fasting blood glucose level is between 126-140 mg/dL.
**Correct Answer:** C. 126 mg/dL.