How to Explain Hemoglobin A1c to a Patient
Hemoglobin A1c is a blood test that shows your average blood sugar level over the past 2-3 months by measuring how much sugar has attached to the hemoglobin protein inside your red blood cells. 1
The Basic Concept
Think of hemoglobin as a taxi driver in your blood—it carries oxygen throughout your body. 1 When sugar (glucose) is floating around in your bloodstream, some of it naturally sticks to the hemoglobin, like dust sticking to a car. 1 The more sugar in your blood over time, the more sugar sticks to the hemoglobin. 1
Why 2-3 Months?
- Red blood cells live for about 120 days (roughly 3-4 months) before your body replaces them with new ones. 1
- The A1c test measures the percentage of your hemoglobin that has sugar attached to it during this lifespan. 1
- This gives us a "memory" of your average blood sugar over approximately the past 60-90 days, not just what it is today. 1
Understanding Your Number
The A1c result is reported as a percentage—the higher the percentage, the higher your average blood sugar has been. 1
What the Numbers Mean:
- Below 5.7%: Normal, no diabetes 1
- 5.7% to 6.4%: Prediabetes (high risk for developing diabetes) 1
- 6.5% or higher: Diabetes 1
- Target for most people with diabetes: Below 7% 1
Converting to Average Blood Sugar
Your A1c percentage can be translated into an average blood sugar number that matches what you see on your glucose meter at home. 1 For example:
- A1c of 6% = average blood sugar of 126 mg/dL 1
- A1c of 7% = average blood sugar of 154 mg/dL 1
- A1c of 8% = average blood sugar of 183 mg/dL 1
- A1c of 9% = average blood sugar of 212 mg/dL 1
- A1c of 10% = average blood sugar of 240 mg/dL 1
Each 1% change in A1c equals approximately a 29 mg/dL change in average blood sugar. 1
Why This Test Matters
- It predicts your risk for diabetes complications like eye disease, kidney disease, nerve damage, and heart disease—the higher your A1c, the higher your risk. 1
- It shows how well your diabetes treatment is working over time, not just on one particular day. 1
- It's more stable than daily blood sugar checks, which can vary dramatically based on what you ate, stress, illness, or exercise. 1
Important Limitations to Know
When A1c May Not Be Accurate:
- If you have anemia or blood loss, your A1c may be falsely low because your red blood cells don't live as long. 1, 2
- If you have certain blood disorders (like sickle cell trait or thalassemia), the test may give incorrect results. 1, 3
- If you've had a recent blood transfusion, the A1c won't reflect your true blood sugar control. 4
In these situations, your doctor should rely more on your daily blood sugar readings instead. 1, 4
What A1c Doesn't Tell You:
- It doesn't show blood sugar swings—you could have dangerous highs and lows that average out to look "normal." 1
- It doesn't detect low blood sugar episodes (hypoglycemia). 1
- Small changes (±0.3%) may just be test variation, not a real change in your control. 1
How Often to Check
- Every 3 months if your treatment has changed or you're not meeting your goals. 1
- Every 6 months if your diabetes is well-controlled and stable. 1
The Bottom Line
The A1c test is like a report card for your diabetes management—it tells you how you've been doing overall, not just how you did on one test day. 1 By keeping your A1c in the target range (usually below 7%), you significantly reduce your risk of serious diabetes complications. 1