HbA1c (Glycated Hemoglobin)
Definition
HbA1c (hemoglobin A1c) measures the percentage of hemoglobin proteins in blood that have glucose attached. It reflects average blood glucose levels over the preceding 2-3 months.
Why It Matters
HbA1c is a cornerstone of diabetes management: - Long-term glucose control - Not affected by daily fluctuations - Diabetes diagnosis - Diagnostic threshold ≥6.5% - Complication risk - Higher HbA1c predicts microvascular complications - Treatment targets - Guides medication adjustments - Mortality predictor - Both high and very low HbA1c associated with increased mortality
Reference Values
| HbA1c | Interpretation |
|---|---|
| <5.7% | Normal |
| 5.7-6.4% | Prediabetes |
| ≥6.5% | Diabetes (requires confirmation) |
Treatment Targets (Diabetes)
| Target | Population |
|---|---|
| <7.0% | Most adults with diabetes |
| <6.5% | Some patients if achievable without hypoglycemia |
| <8.0% | Elderly, limited life expectancy, hypoglycemia risk |
Individual targets should be set with healthcare provider.
Estimated Average Glucose (eAG)
HbA1c can be converted to estimated average glucose:
| HbA1c | eAG (mg/dL) | eAG (mmol/L) |
|---|---|---|
| 5.0% | 97 | 5.4 |
| 6.0% | 126 | 7.0 |
| 7.0% | 154 | 8.6 |
| 8.0% | 183 | 10.2 |
| 9.0% | 212 | 11.8 |
| 10.0% | 240 | 13.4 |
How It's Measured
- Lab blood test - Standard venous blood draw
- Point-of-care devices - Some clinics have rapid testing
- Home tests - Some approved home HbA1c kits available
HealthKit: Can store lab results from clinical records integration.
Confounders & Limitations
Conditions affecting HbA1c accuracy: - Anemia - Can falsely lower HbA1c - Hemoglobin variants - Affects some assays - Recent blood loss/transfusion - Alters results - Kidney disease - Can affect accuracy - Pregnancy - Lower HbA1c due to increased RBC turnover - Iron deficiency - May falsely elevate HbA1c
Use Cases
- Diabetes screening - Part of diagnostic criteria
- Treatment monitoring - Assess glucose control over time
- Medication adjustment - Guide therapy changes
- Risk assessment - Predict complication risk
- Trend tracking - Monitor progress over months/years
Testing Frequency
- No diabetes: Per screening guidelines (typically every 3 years if normal)
- Prediabetes: Annually
- Diabetes, stable: Every 6 months
- Diabetes, changing treatment: Every 3 months
Relationship to Daily Glucose
HbA1c reflects average glucose but doesn't show: - Hypoglycemia episodes - Glucose variability - Time in range - Post-meal spikes
For complete picture, combine with CGM data if available.