What is a good fasting blood sugar level?

Normal Fasting Blood Sugar Levels

A good fasting blood sugar level is between 70-99 mg/dL (3.9-5.5 mmol/L) for most adults without diabetes. 1

Normal Blood Glucose Ranges

• Fasting blood glucose less than 100 mg/dL (5.6 mmol/L) is considered normal 1
• Values between 100-125 mg/dL (5.6-6.9 mmol/L) indicate impaired fasting glucose, also known as "prediabetes" 1, 2
• Fasting blood glucose of 126 mg/dL (7.0 mmol/L) or higher on two separate occasions is diagnostic for diabetes 1

Optimal Targets for Different Populations

For People Without Diabetes:

• Ideal fasting blood glucose is typically below 100 mg/dL (5.6 mmol/L) 1
• Research suggests that even within the normal range, levels of 87-99 mg/dL (4.83-5.5 mmol/L) may indicate increased risk for future diabetes compared to lower values 3

For People With Diabetes:

• Target fasting blood glucose range is typically 80-130 mg/dL (4.4-7.2 mmol/L) 1
• More stringent goals of 110-140 mg/dL (6.1-7.8 mmol/L) may be appropriate for selected patients if they can be achieved without significant hypoglycemia 1
• For hospitalized patients with diabetes, a target glucose range of 140-180 mg/dL (7.8-10.0 mmol/L) is recommended 1

Factors Affecting Fasting Blood Glucose

• Biological variation in fasting glucose can range from 4.8% to 6.1% within the same person on different days 1
• For a true fasting glucose of 100 mg/dL, normal biological variation means values could range from 87-113 mg/dL on different days 1
• Factors that can affect fasting blood glucose include:
  • Stress and illness 1
  • Medications (especially glucocorticoids) 1
  • Recent food intake (improper fasting) 1
  • Time of day 1

Clinical Significance of Fasting Blood Glucose

• Fasting blood glucose below 100 mg/dL (5.6 mmol/L) is associated with lower risk of developing type 2 diabetes 3
• In individuals with mild hyperglycemia (fasting glucose <140 mg/dL), the primary issue is decreased efficiency in tissue glucose uptake 4
• In those with more severe hyperglycemia (>140 mg/dL), elevated hepatic glucose production becomes the major factor 4
• Research suggests that targeting fasting blood glucose between 3.9-6.1 mmol/L (70-110 mg/dL) may be optimal for achieving HbA1c goals in people with type 2 diabetes 5

Common Pitfalls in Measuring Fasting Blood Glucose

• Not fasting for at least 8 hours before the test 1
• Using point-of-care glucose meters, which may be less accurate than laboratory analyzers 1
• Failing to consider normal biological variation when interpreting a single reading 1
• Not confirming abnormal results with a second test on a different day 1

Remember that while these ranges provide general guidance, individual targets may vary based on age, comorbidities, and other health factors. For people with diabetes, treatment goals should be determined in consultation with healthcare providers.