Good Fasting Blood Glucose Levels
For individuals without diabetes, a good fasting blood glucose is 70-100 mg/dL, while those with established diabetes should target 80-130 mg/dL for optimal management. 1, 2
For People Without Diabetes
Normal Range
- Fasting glucose of 70-100 mg/dL is considered normal, with postprandial values remaining below 140 mg/dL 1-2 hours after meals. 2
Prediabetes (Increased Risk Zone)
- Fasting glucose of 100-125 mg/dL defines prediabetes (also called impaired fasting glucose), indicating significantly elevated risk for developing diabetes. 1, 2
- The American Diabetes Association uses 100 mg/dL as the lower threshold, though the World Health Organization uses 110 mg/dL, reflecting that this cutoff represents statistical convenience rather than a biological cliff. 3
- Even within the "normal" range, higher fasting glucose levels (87-99 mg/dL) progressively increase diabetes risk, particularly when combined with obesity or elevated triglycerides. 4
Diabetes Diagnosis
- Fasting glucose ≥126 mg/dL on two separate occasions confirms diabetes, measured after at least 8 hours without caloric intake. 1, 2
For People With Established Diabetes
Outpatient Management Targets
- Target fasting/preprandial glucose of 80-130 mg/dL for most non-pregnant adults with diabetes to achieve HbA1c <7.0% and reduce microvascular complications. 1
- Postprandial glucose should remain <180 mg/dL. 1, 2
Age-Based Individualization
For older adults with diabetes, targets should be adjusted based on health status: 1
- Healthy older adults: 80-130 mg/dL fasting
- Complex/intermediate health: 90-150 mg/dL fasting
- Very complex/poor health: 100-180 mg/dL fasting
Hospital Settings
- Hospitalized patients (both critically ill and non-critically ill) should target 140-180 mg/dL, with insulin therapy initiated when glucose persistently exceeds 180 mg/dL. 5, 1
- More stringent goals of 110-140 mg/dL may be appropriate for selected patients (e.g., post-surgical) if achievable without significant hypoglycemia. 5
Critical Thresholds to Recognize
Hypoglycemia
- Glucose <70 mg/dL requires immediate treatment with 15-20g fast-acting carbohydrate, then recheck in 15 minutes. 1, 2
- Glucose <54 mg/dL represents clinically significant hypoglycemia with neuroglycopenic symptoms requiring urgent intervention. 1, 2
Important Caveats
- Fasting glucose has 12-15% day-to-day variability, meaning the same person could measure 99 mg/dL one day and 110 mg/dL the next without actual metabolic change. 3
- Diagnosis requires confirmation with a second abnormal test unless unequivocal hyperglycemia or classic symptoms are present. 5, 3
- The 1 mg/dL difference between 99 and 100 mg/dL is clinically arbitrary—risk increases gradually across the entire range rather than at a specific cutoff. 3
- Fasting glucose <100 mg/dL in hospitalized patients predicts hypoglycemia risk within 24 hours. 5