A1C
Also known as: HbA1c, Hemoglobin A1c, Glycated hemoglobin, Glycohemoglobin
A1C is a blood test that measures average blood sugar levels over the past 2-3 months by detecting glycated hemoglobin. Also called HbA1c or hemoglobin A1c, it is the primary endpoint in diabetes medication trials and a key indicator of glycemic control.
Last updated: January 28, 2026
What is A1C?
A1C (also called HbA1c or hemoglobin A1c) is a blood test that measures the percentage of hemoglobin proteins in red blood cells that have glucose attached. Because red blood cells live approximately 120 days, A1C reflects average blood sugar levels over the past 2-3 months.
Key concept: A1C is the gold standard for assessing long-term blood sugar control and is the primary endpoint in most diabetes medication clinical trials.
How A1C Works
The glycation process:
- Glucose in blood attaches to hemoglobin in red blood cells
- Higher blood glucose = more glycated hemoglobin
- Glycation is proportional to average glucose exposure
- Test measures percentage of glycated hemoglobin
A1C Interpretation
| A1C Level | Interpretation |
|---|---|
| Under 5.7% | Normal |
| 5.7-6.4% | Prediabetes |
| 6.5% or higher | Diabetes diagnosis |
| Under 7.0% | Typical treatment target |
| Under 8.0% | Target for some populations |
A1C to Average Blood Sugar
| A1C (%) | Estimated Average Glucose (mg/dL) |
|---|---|
| 5.0 | 97 |
| 6.0 | 126 |
| 7.0 | 154 |
| 8.0 | 183 |
| 9.0 | 212 |
| 10.0 | 240 |
A1C in Peptide Research
A1C reduction is the primary efficacy endpoint for diabetes medications:
| Medication | Maximum A1C Reduction |
|---|---|
| Tirzepatide 15 mg | -2.6% |
| Semaglutide 2 mg | -2.0% |
| Liraglutide 1.8 mg | -1.5% |
| Dulaglutide 4.5 mg | -1.6% |
Why A1C Matters
Clinical significance:
- Every 1% A1C reduction → ~35% reduction in microvascular complications
- Associated with reduced risk of nephropathy, retinopathy, neuropathy
- Cardiovascular risk also correlates with A1C
Regulatory importance:
- FDA requires A1C reduction for diabetes drug approval
- Primary endpoint in SUSTAIN (semaglutide), SURPASS (tirzepatide), LEADER trials
A1C Limitations
| Limitation | Explanation |
|---|---|
| Time lag | Reflects past, not current glucose |
| Hemoglobinopathies | Sickle cell, thalassemia can affect results |
| Anemia | Altered red blood cell turnover |
| Pregnancy | Unreliable during pregnancy |
| Variability | Doesn’t capture glucose fluctuations |
Alternative Glucose Metrics
| Test | Measures | Timeframe |
|---|---|---|
| Fasting glucose | Single point | Moment |
| 2-hour OGTT | Post-glucose load | 2 hours |
| CGM (continuous) | Real-time glucose | Days-weeks |
| Time in range | % in target range | Days-weeks |
| Fructosamine | Glycated proteins | 2-3 weeks |
This entry is for educational purposes only. A1C targets should be individualized. Consult a healthcare provider for medical advice.
Related Peptides
Related Terms
Disclaimer: This glossary entry is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider for medical questions.