FBS (Fasting Blood Sugar): Definition, Procedure & Significance

FBS = Fasting Blood Sugar – blood glucose measured after 8–12 hour overnight fast.

Purpose

• Diagnose diabetes (FBS ≥126 mg/dL on two occasions)
• Monitor glycemic control in diabetes
• Assess baseline glucose regulation

Physiology

During fasting, glycogen depletes; liver produces glucose (gluconeogenesis) to maintain levels. FBS reflects this baseline.

Interpretation

• Normal: <100 mg/dL
• Prediabetes: 100–125 mg/dL
• Diabetes: ≥126 mg/dL

Confirm with repeat testing or HbA1c.