HbA1c might show high blood sugar even in people who actually have normal levels, because some people's red blood cells live longer than usual.

Sometimes, blood sugar tests that don’t use HbA1c might give a better picture of how well someone’s diabetes is managed—especially if things like blood disorders or other health issues make the standard HbA1c test less reliable.

HbA1c tells you how much sugar has been sticking to your blood cells over the past few months — it's like a long-term blood sugar report card.

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 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.

Doctors usually rely on the HbA1c blood test to see how well someone with diabetes has managed their blood sugar over time — but some experts are starting to question if it’s always accurate for everyone.