Normal Capillary Blood Glucose Ranges
For healthy adults and children without diabetes, normal fasting capillary blood glucose is 70–100 mg/dL (3.9–5.6 mmol/L), and postprandial glucose should remain below 140 mg/dL (7.8 mmol/L) at 2 hours after eating. 1, 2
Fasting Glucose Values
- Normal fasting capillary glucose: 70–100 mg/dL (3.9–5.6 mmol/L) 2, 3
- Impaired fasting glucose (prediabetes): 100–125 mg/dL (5.6–6.9 mmol/L) 2
- Diabetes threshold: ≥126 mg/dL (7.0 mmol/L) on two separate occasions 1, 2
Postprandial (After-Meal) Glucose Values
- Normal 2-hour postprandial glucose: <140 mg/dL (7.8 mmol/L) 1, 2
- Impaired glucose tolerance (prediabetes): 140–199 mg/dL (7.8–11.0 mmol/L) at 2 hours 1, 2
- Diabetes threshold: ≥200 mg/dL (11.1 mmol/L) at 2 hours 1
- Peak postprandial glucose in healthy individuals: typically 110 mg/dL (6.1 mmol/L), occurring 30–60 minutes after eating 1
Special Populations
Neonates and Infants
- First few hours of life: 1.4–6.2 mmol/L (25–112 mg/dL) is normal 3
- By 72 hours of age: fasting glucose stabilizes to 3.5–5.5 mmol/L (63–99 mg/dL), matching adult values 3
Gestational Diabetes Targets
- Fasting: <95 mg/dL (5.3 mmol/L) 4
- 1-hour postprandial: ≤140 mg/dL (7.8 mmol/L) 1
- 2-hour postprandial: ≤120 mg/dL (6.7 mmol/L) 1
Important Clinical Considerations
Hypoglycemia Threshold
- Clinically significant hypoglycemia: <70 mg/dL (3.9 mmol/L) requires treatment with 15 g fast-acting carbohydrate 5
- Severe hypoglycemia: <54 mg/dL (3.0 mmol/L) indicates neuroglycopenic threshold requiring immediate action 5
Capillary vs. Venous Sampling
- Capillary and venous glucose values are comparable in healthy, non-fasted individuals when using point-of-care glucometers, with a mean difference of only 0.3 mmol/L (5.4 mg/dL) 6
- In critically ill patients with hypoperfusion, shock, or vasopressor use, arterial or venous sampling is preferred over finger-stick capillary testing because capillary values may be unreliable 5
Timing of Measurements
- Fasting glucose: measured after at least 8 hours without caloric intake 2
- Postprandial glucose: measured 1–2 hours after the start of a meal, when peak levels typically occur 5, 1
Common Pitfalls to Avoid
- Do not diagnose diabetes based on a single elevated reading; confirmation requires repeat testing on a separate day 2
- Do not ignore postprandial values; some individuals have normal fasting glucose but elevated postprandial excursions indicating impaired glucose tolerance 1, 4
- Do not rely on capillary finger-stick testing in patients with shock, severe edema, or on vasopressors, as peripheral hypoperfusion causes unreliable readings 5
- Do not use a single glucose threshold to define hypoglycemia in neonates; clinical context and counter-regulatory responses must be considered 3