## **Core Concept**
The question tests understanding of glucose metabolism and diagnostic criteria for diabetes mellitus. Postprandial blood glucose levels are an important indicator of glucose regulation in the body. The American Diabetes Association (ADA) and World Health Organization (WHO) provide guidelines for the diagnosis of diabetes based on blood glucose levels.

## **Why the Correct Answer is Right**
The correct answer, <140 mg/dL, is based on the diagnostic criteria established by the ADA and WHO. A postprandial blood glucose level of less than 140 mg/dL is considered normal. Levels between 140-199 mg/dL indicate impaired glucose tolerance, and levels ≥200 mg/dL are diagnostic of diabetes mellitus. This criterion helps in the early detection and management of diabetes. ## **Why Each Wrong Option is Incorrect** - **Option A:** <100 mg/dL - This is too low and actually represents a fasting blood glucose level that is considered normal or the target for individuals with diabetes. - **Option B:** <120 mg/dL - While closer, this is still lower than the established threshold for a normal postprandial glucose level. - **Option D:** <200 mg/dL - This option is incorrect because it includes levels that are diagnostic of diabetes mellitus (≥200 mg/dL) and impaired glucose tolerance (140-199 mg/dL). ## **Clinical Pearl / High-Yield Fact** A key point to remember is that the diagnosis of diabetes can be made based on either a fasting blood glucose level ≥126 mg/dL or a 2-hour postprandial blood glucose level ≥200 mg/dL during an oral glucose tolerance test (OGTT). For clinical practice, it's essential to know these thresholds to diagnose and manage diabetes effectively. ## **Correct Answer:** . <140 mg/dL