Blood Glucose
Definition
The concentration of glucose (sugar) in the blood, typically measured in mg/dL (US) or mmol/L (international).
Conversion: 1 mmol/L = 18 mg/dL
Why It Matters
Blood glucose is central to metabolic health: - Diabetes diagnosis - Elevated glucose indicates diabetes - Diabetes management - Daily monitoring for treatment - Prediabetes detection - Early intervention opportunity - Metabolic health - Blood sugar regulation reflects overall health - Energy levels - Glucose is the body's primary fuel
How It's Measured
- Fingerstick meters - Traditional home glucose monitors
- Continuous Glucose Monitors (CGM) - Real-time tracking (Dexcom, Libre, etc.)
- Lab tests - Clinical blood draws
- Data sources - Many glucose devices sync to HealthKit
Reference Values (Fasting)
| Category | Fasting Glucose |
|---|---|
| Normal | <100 mg/dL (<5.6 mmol/L) |
| Prediabetes | 100-125 mg/dL (5.6-6.9 mmol/L) |
| Diabetes | ≥126 mg/dL (≥7.0 mmol/L) |
HbA1c (long-term average): - Normal: <5.7% - Prediabetes: 5.7-6.4% - Diabetes: ≥6.5%
Confounders & Limitations
- Timing - Fasting vs post-meal readings differ significantly
- Stress - Acute stress elevates glucose
- Medications - Steroids, some drugs affect glucose
- Illness - Infections can raise glucose
- Sample handling - Improper technique affects accuracy
- Meter accuracy - Consumer devices have ±15% tolerance
Use Cases
- Diabetes monitoring - Daily management
- Prediabetes tracking - Lifestyle intervention assessment
- Dietary impact - How foods affect your glucose
- CGM trends - Time in range, variability
- Medical visits - Sharing data with healthcare team
Time in Range (CGM Users)
Target for most diabetics: - In range (70-180 mg/dL): >70% of time - Below range (<70): <4% of time - Above range (>180): <25% of time
When to Seek Care
- Fasting glucose consistently >100 mg/dL
- Symptoms of high glucose (thirst, frequent urination, fatigue)
- Symptoms of low glucose (shakiness, confusion, sweating)
- Difficulty achieving target ranges
- Any glucose >300 mg/dL or <54 mg/dL