If your red blood cells live longer, they soak up more sugar over time, which can make your HbA1c blood test go up — even if your average blood sugar hasn't actually changed.

If your body is healthier and your red blood cells live longer, your HbA1c blood sugar test might show higher levels — not because your blood sugar is high, but because the sugar has more time to stick to older red blood cells.

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 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 you have type 2 diabetes, higher blood sugar might make your red blood cells die faster, which could mess up the accuracy of your A1c test — a common way doctors check long-term blood sugar control.

If someone with type 2 diabetes has red blood cells that don't live as long as usual, their A1c test might show better blood sugar control than they actually have — meaning doctors could miss signs of high blood sugar over time.