If your red blood cells live longer or shorter than average, your A1C test might not give a true picture of your average blood sugar levels.

If someone with type 2 diabetes has good HbA1c numbers but their red blood cells don’t live as long, their blood sugar might actually be higher than the test shows — meaning the test could be giving them a too-rosy picture of their sugar control.

Your HbA1c number isn't just about your average blood sugar — it also depends on how long your red blood cells live. The longer they stick around, the more sugar builds up on them, which can raise your HbA1c even if your blood sugar is stable.

If you have type 2 diabetes and your red blood cells don’t live as long—less than 75 days—your A1c test might not give a true picture of your blood sugar control, because the test could show lower numbers than reality.

If your red blood cells live longer than usual, your A1C test might show high blood sugar even if your actual sugar levels are normal.

If you have type 2 diabetes and your red blood cells don’t live as long, your actual blood sugar might be higher than what your A1c test shows — meaning the A1c test could be misleading for some people.