Your A1C is a blood test result that reflects your average blood sugar over the past two to three months. It’s reported as a percentage: below 5.7% is normal, 5.7% to 6.4% indicates prediabetes, and 6.5% or higher means diabetes. Unlike a finger-stick glucose reading that captures a single moment, A1C gives you and your doctor a longer view of how your body has been handling sugar.
How the A1C Test Works
Hemoglobin is the protein inside red blood cells that carries oxygen. As blood sugar circulates, glucose naturally attaches to hemoglobin in a process called glycation. The higher your blood sugar runs day after day, the more glucose coats your hemoglobin, and the higher your A1C percentage climbs.
Red blood cells live for about three months before your body replaces them. That turnover is what gives A1C its measurement window. The test essentially reads the sugar buildup on red blood cells of varying ages, producing a weighted average that reflects the last 8 to 12 weeks of blood sugar levels, with the most recent weeks carrying more influence than the earliest ones.
What Your Number Means
The CDC uses these ranges for diagnosis:
- Below 5.7%: Normal blood sugar control
- 5.7% to 6.4%: Prediabetes
- 6.5% or higher: Diabetes
You can also translate your A1C into an estimated average glucose (eAG), which is the number you’d see on a blood sugar meter. The conversion formula multiplies your A1C by 28.7, then subtracts 46.7. So an A1C of 6.0% corresponds to an average blood sugar of about 126 mg/dL. At 7.0%, that average jumps to roughly 154 mg/dL. At 8.0%, it’s around 183 mg/dL. Many lab reports now print the eAG alongside your A1C to make the result more intuitive.
Your Target May Not Be 6.5%
The diagnostic cutoff for diabetes is 6.5%, but your personal treatment target depends on your situation. The American Diabetes Association sets a general goal of below 7% for most adults with diabetes. For healthy older adults, the target relaxes to below 7.5%. For older adults with multiple health conditions or limited life expectancy, targets of below 8% or even 8.5% are considered appropriate.
The reasoning is straightforward: pushing blood sugar very low with medication carries its own risks, especially dangerous drops in blood sugar (hypoglycemia). For someone who is younger, otherwise healthy, and recently diagnosed, tighter control pays off in fewer long-term complications. For someone who is older with other serious health conditions, the risks of aggressive treatment can outweigh the benefits. Your target should be a conversation, not a one-size-fits-all number.
How Often You Should Test
If you have diabetes and your blood sugar is stable and on target, testing twice a year is the standard recommendation. If your treatment plan has recently changed or you’re not meeting your goals, testing every three months gives you and your doctor faster feedback on whether adjustments are working.
For people without diabetes, A1C is typically checked during routine bloodwork or when risk factors like obesity, family history, or age warrant screening.
No Fasting Required
One of the practical advantages of the A1C test is that you don’t need to fast beforehand. Because it measures glucose buildup over months rather than a snapshot of current blood sugar, eating before the test won’t change the result. Stress, exercise, and what you ate for breakfast that morning also have no effect. You can have it drawn at any time of day, during any appointment.
When A1C Results Can Be Misleading
The test assumes your red blood cells have a normal lifespan. Several conditions alter that assumption, pushing your result artificially high or low.
Iron deficiency anemia is one of the most common causes of a falsely elevated A1C. When you’re low on iron, your red blood cells stick around longer than usual, giving glucose more time to accumulate on hemoglobin. Vitamin B-12 and folate deficiency anemias have the same effect. On the other hand, conditions that destroy red blood cells faster, like hemolytic anemia or significant blood loss, produce falsely low readings because the cells don’t live long enough to accumulate a representative amount of glucose.
Kidney disease, particularly end-stage renal disease, tends to pull A1C results downward. The chronic anemia that accompanies kidney failure shortens red blood cell survival, meaning the test underestimates true average blood sugar. Uremia (toxin buildup from poor kidney function) can also interfere with the chemical assay itself, sometimes nudging results in the opposite direction.
Pregnancy changes A1C in ways that make it unreliable for diagnosing gestational diabetes. Red blood cell lifespan shortens to about 90 days, and increased blood cell production dilutes the reading further. A1C values typically drop by 12 to 16 weeks of gestation and continue declining until around week 20 to 24 before rising slightly in the third trimester. Pregnant women are screened with a glucose tolerance test instead.
Hemoglobin variants, most commonly hemoglobin S (sickle cell) and hemoglobin C, can push results in either direction depending on the variant and the testing method used. People who carry the trait (one copy) can usually get reliable A1C results with the right lab technique. People with two copies of the variant gene generally need an alternative test entirely.
Home A1C Kits
Over-the-counter A1C test kits let you check your level with a finger prick at home. They can be useful for tracking trends between doctor visits, but they’re less precise than lab-drawn blood. The accuracy standard for these kits allows results to fall within roughly 13.5% of the lab reference value. In practical terms, that means a home kit reading of 7.0% could reflect a true lab value anywhere from about 6.1% to 7.9%. That margin is wide enough to matter when you’re making treatment decisions, so home kits work better as a general check-in than as a substitute for lab testing.
What Moves Your A1C
Because A1C tracks average blood sugar over months, it responds to sustained changes in diet, activity, and medication rather than short-term efforts. Cutting back on refined carbohydrates, increasing physical activity, losing even a modest amount of weight, and taking prescribed medications consistently are the levers that move the number over time. Most people see meaningful changes reflected in their next test three months later.
It’s also worth knowing that A1C captures averages, not swings. Two people could have the same A1C of 7.0% while experiencing very different daily patterns: one with stable blood sugar hovering around 154 mg/dL, and another swinging between 60 and 250 mg/dL. If you use a continuous glucose monitor or check blood sugar at home, those readings add context that A1C alone can’t provide.