Glucose testing
1. Diagnostic Thresholds (Venous Plasma)
Diagnosis is typically based on two separate abnormal tests (unless symptomatic).
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| Fasting Plasma Glucose (FPG) | <5.6 mmol/L | 5.6–6.9 mmol/L | ≥7.0 mmol/L |
| 2-hr OGTT (75g load) | <7.8 mmol/L | 7.8–11.0 mmol/L | ≥11.1 mmol/L |
| HbA1c | <42 mmol/mol (6.0%) | 42–47 mmol/mol (6.0–6.4%) | ≥48 mmol/mol (≥6.5%) |
| Random Glucose | N/A | N/A | ≥11.1 mmol/L (+ symptoms) |
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Note: HbA1c may be unreliable in conditions with high red cell turnover (e.g., hemolytic anemia, pregnancy, recent hemorrhage).
2. Glycemic Targets for Management
Targets are individualized based on age, comorbidities, and hypoglycemia risk.
Capillary Blood Glucose (CBG) Targets:
- Type 1 Diabetes (Adults):
- Fasting/Pre-prandial: 4.0–7.0 mmol/L
- Post-prandial (90 min+): 5.0–9.0 mmol/L
- Type 2 Diabetes:
- Pre-prandial: 4.0–7.0 mmol/L
- Post-prandial: <8.5 mmol/L
- Pregnancy (GDM/Pre-existing): * Fasting: <5.3 mmol/L
- 1-hr Post-prandial: <7.8 mmol/L
HbA1c Maintenance Targets:
- Type 2 (Diet/Monotherapy): 48 mmol/mol (6.5%)
- Type 2 (on Hypo-inducing meds): 53 mmol/mol (7.0%)
3. Modern Testing Modalities
- Continuous Glucose Monitoring (CGM): Now the standard for T1D and many T2D patients on insulin. Focuses on Time in Range (TIR), typically aiming for >70% of readings between 3.9 and 10.0 mmol/L.
- Flash Glucose Monitoring: Intermittent scanning (e.g., FreeStyle Libre).
- Glucose Management Indicator (GMI): A CGM-derived estimate of HbA1c.
4. Acute Critical Values
- Hypoglycemia: <4.0 mmol/L ("Four is the Floor").
- Hyperglycemic Crisis: Random glucose >33.3 mmol/L suggests Hyperosmolar Hyperglycemic State (HHS) or Diabetic Ketoacidosis (DKA) if ketones are present (>3.0 mmol/L).
Would you like me to go into the specific pathophysiology of HbA1c discordance or the latest 2026 ADA/NICE updates on CGM metrics?