Understanding Normal Blood Sugar Levels: Ranges & What They Mean
Blood glucose targets vary by context. Values below refer to venous plasma (lab standard).
Diagnostic Criteria (ADA / WHO)
| Test | Normal | Prediabetes | Diabetes |
|---|
| Fasting (≥8 hr) | < 100 mg/dL (5.6 mmol/L) | 100–125 mg/dL (5.6–6.9) | ≥126 mg/dL (7.0) on 2 occasions |
| Random + symptoms | — | — | ≥200 mg/dL (11.1) |
| OGTT 2-hr (75g) | < 140 mg/dL (7.8) | 140–199 mg/dL (7.8–11.0) | ≥200 mg/dL (11.1) |
| HbA1c | < 5.7% | 5.7–6.4% | ≥6.5% |
Physiologic Ranges (Non-Diabetic)
- Fasting: 70–99 mg/dL
- Postprandial (1–2 hr): <140 mg/dL
- Mean 24-hr (CGM): 89–104 mg/dL
- Time in range (70–180): >70% (non-diabetic >95%)
Key Nuances
- Units: mg/dL (US) vs. mmol/L (international) — divide mg/dL by 18.
- Fasting definition: No calories ≥8 hrs; water ok.
- OGTT protocol: 3-day carb prep (≥150g/d), overnight fast, 75g glucose load.
- HbA1c limitations: Anemia, hemoglobinopathies, pregnancy, renal failure, recent transfusion alter accuracy.
- Individual targets: Older adults, comorbidities, hypoglycemia risk → less stringent (e.g., HbA1c <8%).
When to Test
- Screening: Age 35+ (or earlier with risk factors: BMI ≥25, family history, ethnicity, GDM, PCOS, etc.).
- Symptoms: polyuria, polydipsia, weight loss, fatigue, blurred vision.
- Monitoring: per provider plan if diabetic/prediabetic.
Always interpret results with your clinician—context defines significance.
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