Normal Blood Glucose Levels: Fasting, Postprandial, and Diagnostic Thresholds

Blood glucose concentration is tightly regulated (70–110 mg/dL fasting).

Reference Ranges (Venous Plasma)

• Fasting (8+ hours): 70–99 mg/dL (3.9–5.5 mmol/L) – normal. 100–125 = impaired fasting glucose (IFG). ≥126 = diabetes (confirm repeat).
• Postprandial (2h after 75g OGTT): <140 mg/dL (7.8 mmol/L) – normal. 140–199 = impaired glucose tolerance (IGT). ≥200 = diabetes.
• Random + symptoms: ≥200 mg/dL = diabetes.
• HbA1c: <5.7% normal; 5.7–6.4% prediabetes; ≥6.5% diabetes.

Percentage Expression

Glucose is ~0.1% of blood weight (100 mg/dL = 100 mg/100g = 0.1%). The source's 0.07–0.11% and <0.14% are equivalent.

Physiological Regulation

• Insulin (β-cells): ↓ glucose via GLUT4 translocation, glycogen synthesis, lipogenesis.
• Glucagon (α-cells): ↑ glucose via glycogenolysis, gluconeogenesis.
• Incretins (GLP-1, GIP): amplify insulin, suppress glucagon.
• Counterregulatory: cortisol, epinephrine, GH.

Monitoring

SMBG (fingerstick), CGM (continuous), HbA1c (3-month average). Targets individualized (ADA: 80–130 premeal, <180 postprandial for many).