HbA1c (Hemoglobin A1c): Normal Range, What High & Low Levels Mean

Your HbA1c test measures the percentage of haemoglobin — a protein inside your red blood cells — that has glucose (sugar) attached to it. Because red blood cells live for approximately two to three months, this percentage acts like an average diary of your blood sugar levels over that whole period, rather than a single-day reading. Doctors use it to diagnose prediabetes and diabetes and to track how well blood sugar management is working over time. Talk with your healthcare provider about what your specific result means for your health.

According to the American Diabetes Association, an HbA1c below 5.7% is considered normal, meaning blood sugar has been in a healthy range on average. A reading between 5.7% and 6.4% signals prediabetes — higher than ideal, but not yet at a diabetes diagnosis. A result of 6.5% or above meets the diagnostic threshold for diabetes. For people already managing diabetes, a common treatment target is 7% or below, though individual targets vary. Reference ranges can also be affected by certain medical conditions, so always discuss your specific number with your healthcare provider.

The most common reasons for an elevated HbA1c are type 2 diabetes and type 1 diabetes, where the body either doesn't produce enough insulin or can't use it properly, leaving excess glucose circulating in the blood and sticking to haemoglobin. Prediabetes with inadequate lifestyle or medication management can also push the number up. In some cases the elevation isn't a true reflection of blood sugar at all — iron deficiency anaemia and chronic kidney disease can both alter red blood cell behaviour in ways that falsely raise HbA1c readings. Your healthcare provider can help you understand the likely cause behind your specific result.

A lower-than-expected HbA1c isn't always good news — it can sometimes be misleading rather than a sign of excellent blood sugar control. Conditions that shorten red blood cell lifespan, such as haemolytic anaemia, cause cells to be replaced faster, so less glucose has time to attach — producing an artificially low reading. A recent blood transfusion introduces donated red cells with no glucose attached, also pulling the number down. Sickle cell disease and other haemoglobin variants can make HbA1c unreliable in either direction. Iron supplementation and hypoglycaemia-prone states are additional factors. Discuss any low reading with your healthcare provider to understand what it means for you.

Persistently elevated blood sugar — reflected in a high HbA1c — can produce a recognisable set of symptoms: increased thirst, frequent urination, unexplained fatigue, blurred vision, slow-healing wounds, frequent infections, and numbness or tingling in the feet or hands. That said, many people with mildly or moderately high HbA1c experience no symptoms at all, which is one reason regular testing matters. Symptoms alone can't tell you your HbA1c level, and a high reading can have more than one cause. If you're experiencing any of these signs alongside an elevated result, speak with your healthcare provider as soon as possible.

How frequently you need an HbA1c test depends on your individual situation — your current result, whether you have a diabetes or prediabetes diagnosis, any recent changes to your medication or lifestyle, and other health factors your doctor tracks. Because the test reflects a two-to-three month average, retesting sooner than that window typically won't capture meaningful change. Some people are tested twice a year; others more or less frequently depending on how stable their blood sugar management is. There is no universal schedule that fits everyone. Your healthcare provider is the right person to set a testing cadence that makes sense for your specific circumstances.