Normal Blood Glucose Levels
For non-pregnant adults without diabetes, normal fasting (morning) blood glucose is less than 100 mg/dL (5.6 mmol/L), and normal 2-hour post-meal glucose is less than 140 mg/dL (7.8 mmol/L).
Fasting Blood Glucose (Morning)
The normal fasting plasma glucose level is <100 mg/dL (<5.6 mmol/L) 1. This measurement should be taken after an overnight fast of at least 8 hours.
Clinical Context:
- Prediabetes range: 100-125 mg/dL (5.6-6.9 mmol/L)
- Diabetes diagnosis: ≥126 mg/dL (≥7.0 mmol/L) on two separate occasions
For individuals with established diabetes on treatment, target fasting glucose varies by population:
- Type 1 diabetes: 80-130 mg/dL (4.4-7.2 mmol/L) premeal 1
- Type 2 diabetes: Similar targets, individualized based on comorbidities
2-Hour Post-Meal (Postprandial) Glucose
The normal 2-hour postprandial glucose is <140 mg/dL (<7.8 mmol/L) 2. This represents the upper limit of normal glucose excursion after eating.
Important Nuances:
The 2-hour postprandial threshold of 140 mg/dL is clinically significant because values above this level, even with normal fasting glucose, are associated with a 2-fold increased risk of cardiovascular death 2. This underscores that isolated postprandial hyperglycemia carries independent cardiovascular risk.
For individuals with diabetes on treatment:
- Type 1 diabetes: Peak postmeal target <180 mg/dL (10.0 mmol/L) 1
- Type 2 diabetes: Similar postprandial targets
Timing Considerations:
While 2-hour postprandial is the standard measurement time, glucose peaks can vary substantially between individuals (range 45-120 minutes after starting a meal) 3. In normal pregnancy, the mean peak postprandial glucose approximates 110 mg/dL (6.1 mmol/L) 3.
Common Pitfalls to Avoid:
- Don't confuse capillary blood glucose with plasma glucose: Modern glucose meters display results corrected to plasma-equivalent values, but older devices may not
- Timing matters: The 2-hour measurement should start from the beginning of the meal, not the end
- Fasting duration: Ensure at least 8 hours of fasting for accurate fasting measurements
- Postprandial hyperglycemia can be missed: Checking only fasting glucose may miss significant postprandial elevations that contribute to cardiovascular risk 2
Note: These values apply to non-pregnant adults. Pregnancy has different, more stringent glucose targets due to effects on fetal development 4, 5.