Which test is primarily used for the diagnosis of diabetes?

• A. Fasting Blood Sugar (FBS)
• B. HbA1c
• C. 1,5-AG
• D. Fructosamine

Answer: (A)

Diagnosing diabetes relies on a clear, reproducible measure of elevated glucose in the fasting state. The fasting plasma glucose test provides this directly after an overnight fast, and it has a well-established cutoff (diabetes diagnosed when the fasting level is 126 mg/dL or higher on two occasions). Its simplicity, low cost, and widespread availability make it the go-to diagnostic tool in many clinical settings. HbA1c can also be used for diagnosis and reflects average glucose over the past 2–3 months, but it can be affected by anemia, hemoglobin variants, and other factors that limit its reliability in some patients. Tests that track short-term fluctuations or intermediate-term glycemia are more for monitoring than for initial diagnosis. So, the fasting blood sugar test is the primary diagnostic choice.