If someone has certain blood conditions like sickle cell trait, their A1c test might show lower blood sugar levels than they actually have, which could trick doctors into thinking diabetes is under control when it's not — especially if they don't also check regular blood sugar tests.

If someone with diabetes has blood sugar numbers that don't match their A1c test, it might be due to a hidden blood condition — even if their blood tests look mostly normal. In those cases, a special blood test could help get the right diagnosis.

If someone with diabetes has confusing blood sugar and A1c results, a special blood test called hemoglobin electrophoresis can help find rare blood conditions that might be messing with their A1c, even if their regular blood tests look mostly normal.

HbA1c shows 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.

In people with a blood disorder who need regular transfusions, the common blood sugar test (HbA1c) often says they have high blood sugar, but their fasting blood sugar test says it's normal — so the two tests don’t match up well.