The question asks to identify the criterion that is NOT used for diagnosing Diabetes Mellitus.

Identifying Diabetes Mellitus Diagnostic Criteria

Accurate diagnosis of Diabetes Mellitus relies on specific blood glucose measurements. Standard diagnostic criteria are established by major health organizations.

Analyzing Diagnostic Options

Let's examine each option against the established diagnostic criteria:

• Option 1: Symptoms of diabetes and random plasma sugar concentration $\ge$ 200 mg/dL
  This is a valid diagnostic criterion. If a person has classic symptoms of hyperglycemia (like increased thirst and urination) and a random plasma glucose level of 200 mg/dL or higher, it indicates diabetes.
• Option 2: HbA1c $\ge$ 6.5 %
  This is another key diagnostic criterion. The HbA1c test reflects average blood glucose levels over the past 2-3 months. A level of 6.5% or higher is diagnostic.
• Option 3: 2-hours plasma glucose $\ge$ 200 mg/dL during an oral glucose tolerance test (OGTT)
  This is also a standard diagnostic criterion. An OGTT measures the body's response to glucose. A 2-hour plasma glucose value of 200 mg/dL or higher after consuming a specific amount of glucose confirms diabetes.
• Option 4: Fasting plasma glucose $\ge$ 110 mg/dL
  This value is NOT the criterion for diagnosing Diabetes Mellitus. The diagnostic threshold for Fasting Plasma Glucose (FPG) is $\ge$ 126 mg/dL (taken after at least 8 hours of fasting). A fasting plasma glucose level between 100 mg/dL and 125 mg/dL indicates Impaired Fasting Glucose (IFG), which is a pre-diabetic state, but not diabetes itself.

Conclusion on Non-Diagnostic Criterion

Based on the analysis, a Fasting Plasma Glucose level of $\ge$ 110 mg/dL is not sufficient on its own to diagnose Diabetes Mellitus.