**Core Concept**
The patient's plasma glucose levels are within the normal range, according to the World Health Organization (WHO) criteria, which states that fasting plasma glucose (FPG) levels < 110 mg/dl and 2-hour post-glucose challenge < 140 mg/dl are considered normal.

**Why the Correct Answer is Right**
The patient's FPG levels are 110 mg/dl on two separate occasions, which is within the normal range. The diagnosis of diabetes mellitus (DM) typically requires two or more abnormal values on different days using the same assay. Since the patient's glucose levels are within normal limits, there is no indication of diabetes mellitus. Fasting plasma glucose is a reliable indicator of glucose metabolism, and normal values can be used to rule out diabetes.

**Why Each Wrong Option is Incorrect**
**Option A:** Declaring the patient as having diabetes mellitus is incorrect because the patient's glucose levels are within the normal range.
**Option B:** Proceeding for oral glucose tolerance test (OGTT) is not necessary in this case since the patient's fasting glucose levels are normal.
**Option D:** Checking for Glycosylated hemoglobin (HbA1c) is not a substitute for FPG measurements. While HbA1c can provide information about long-term glucose control, it is not a direct indicator of diabetes mellitus in this case.

**Clinical Pearl / High-Yield Fact**
Normal fasting plasma glucose levels can be used to rule out diabetes mellitus, especially in patients without symptoms or risk factors for diabetes.

**✓ Correct Answer: C. Declare patient as normal**