Fasting Glucose

Fasting glucose measures the concentration of glucose in the blood after a period without food or caloric beverages, typically at least eight hours.

• Measures blood glucose at a single point in time after fasting.
• Reflects current circulating glucose rather than a long-term average.

• To screen for prediabetes or diabetes.
• To evaluate glucose regulation as part of a metabolic panel.
• To monitor people with known glucose metabolism conditions.

• Reported in mg/dL or mmol/L depending on the country and laboratory.
• Interpreted against fasting-specific reference ranges.

• Ranges vary by laboratory and clinical guideline.
• Commonly, fasting glucose below 100 mg/dL is considered within a typical range, 100-125 mg/dL may suggest impaired fasting glucose, and 126 mg/dL or above may support a diabetes diagnosis.

• Inadequate fasting time can elevate the result.
• Recent illness, stress, and certain medications can affect glucose levels.
• Timing of the draw and hydration status can introduce variability.

• HbA1c reflects a longer-term average and is often used with fasting glucose.
• Lipid panels may be ordered in the same metabolic workup.

• How does my fasting glucose compare to my HbA1c?
• What factors might explain any difference between the two?
• When should I be retested?