Normal Capillary Blood Glucose Ranges
For adults without diabetes, normal capillary blood glucose ranges are: fasting 70-100 mg/dL (3.9-5.6 mmol/L), 2-hour post-meal <140 mg/dL (7.8 mmol/L), and random <140 mg/dL; values consistently above these thresholds warrant further evaluation for prediabetes or diabetes. 1, 2
Fasting Capillary Blood Glucose (Normal Adults)
- Normal fasting capillary blood glucose in adults without diabetes is <100 mg/dL (5.6 mmol/L), measured after at least 8 hours without caloric intake 1
- Values between 100-125 mg/dL (5.6-6.9 mmol/L) indicate impaired fasting glucose (prediabetes), which represents dysglycemia and increased diabetes risk 1
- Fasting values ≥126 mg/dL (7.0 mmol/L) on two separate occasions meet diagnostic criteria for diabetes 1
Post-Prandial Capillary Blood Glucose (Normal Adults)
- Normal 2-hour post-meal capillary blood glucose should be <140 mg/dL (7.8 mmol/L) in individuals without diabetes 1
- Values between 140-199 mg/dL (7.8-11.0 mmol/L) at 2 hours post-glucose load indicate impaired glucose tolerance (IGT) 1
- 2-hour post-prandial values ≥200 mg/dL (11.1 mmol/L) meet diagnostic criteria for diabetes 1
Random Capillary Blood Glucose (Normal Adults)
- Random capillary blood glucose in healthy adults typically remains <140 mg/dL (7.8 mmol/L) throughout the day 1
- Random values ≥200 mg/dL (11.1 mmol/L) with classic symptoms of hyperglycemia (polyuria, polydipsia, weight loss) are diagnostic of diabetes without need for confirmatory testing 1
Normal Ranges for Children and Adolescents
- Children and adolescents without diabetes have the same fasting glucose thresholds as adults: normal <100 mg/dL (5.6 mmol/L) 1
- The 2-hour post-glucose load threshold of ≥200 mg/dL (11.1 mmol/L) for diabetes diagnosis applies equally to pediatric populations 1
- For oral glucose tolerance testing in children, the glucose load should be 1.75 g/kg body weight up to a maximum of 75 g anhydrous glucose 1
Special Considerations for Pregnant Women
- Pregnant women have stricter glycemic targets: fasting <95 mg/dL (5.3 mmol/L), 1-hour post-meal <140 mg/dL (7.8 mmol/L), and 2-hour post-meal <120 mg/dL (6.7 mmol/L) 3
- These lower thresholds reflect the need to prevent fetal macrosomia and other adverse pregnancy outcomes associated with even mild maternal hyperglycemia 3
Critical Technical Considerations
- Capillary blood glucose values differ systematically from venous plasma glucose depending on prandial state: fasting capillary values run approximately 0.1-0.5 mmol/L lower than venous plasma, while post-prandial capillary values run 0.5-1.4 mmol/L higher due to peripheral glucose extraction 4, 5, 6
- Diagnostic criteria for diabetes are based on venous plasma glucose measurements, not capillary whole blood, which can lead to misclassification if equivalence values are not properly applied 4
- Point-of-care glucometers are designed for capillary blood and may show systematic bias when venous blood is used, though the difference is typically not clinically significant in healthy individuals 7
Common Clinical Pitfalls
- Stress hyperglycemia in acutely ill children does not necessarily indicate diabetes, especially in young children with fever or infection; consultation with pediatric endocrinology is warranted before labeling as diabetes 1
- Glucose meters are useful for screening but formal diagnosis of diabetes must be confirmed by measurement of venous plasma glucose on an analytic instrument in a clinical chemistry laboratory 1
- A single elevated glucose value requires confirmation on a separate day unless the patient has classic symptoms of hyperglycemia or is in hyperglycemic crisis 1