**Core Concept**
Diabetes mellitus is a group of metabolic disorders characterized by high blood glucose levels, resulting from defects in insulin secretion, insulin action, or both. Fasting blood glucose (FBG) testing is a widely used method for diagnosing diabetes mellitus.

**Why the Correct Answer is Right**
The correct answer is based on the diagnostic criteria established by the American Diabetes Association (ADA). A fasting blood glucose level of >126 mg/dL is considered diagnostic of diabetes mellitus. This threshold is chosen because it corresponds to a high risk of complications from diabetes, such as cardiovascular disease, kidney damage, and nerve damage. The ADA also provides guidelines for impaired fasting glucose (IFG), which is defined as a FBG level of 110-125 mg/dL.

**Why Each Wrong Option is Incorrect**
**Option A:** A fasting blood glucose level of >100 mg/dL is actually considered the upper limit of normal, and levels in this range may indicate impaired fasting glucose (IFG) rather than diabetes mellitus.
**Option C:** A fasting blood glucose level of >110 mg/dL is considered impaired fasting glucose (IFG), not diabetes mellitus, according to the ADA guidelines.
**Option D:** A fasting blood glucose level of >116 mg/dL is not a commonly recognized threshold for diagnosing diabetes mellitus.

**Clinical Pearl / High-Yield Fact**
When interpreting fasting blood glucose results, it's essential to consider the patient's symptoms and medical history. A single abnormal test result may not be sufficient to diagnose diabetes mellitus, and repeat testing may be necessary to confirm the diagnosis.

**✓ Correct Answer: B. >126. This is the threshold for diagnosing diabetes mellitus according to the American Diabetes Association guidelines.**