An A1C result is a single percentage that represents your average blood sugar over the past two to three months. Below 5.7% is normal, 5.7% to 6.4% falls in the prediabetes range, and 6.5% or higher indicates diabetes. Those three thresholds are the foundation of reading any A1C result, but the number carries more nuance than it first appears.
What the Percentage Actually Measures
Red blood cells contain a protein called hemoglobin that carries oxygen through your bloodstream. When glucose circulates in your blood, some of it attaches to hemoglobin in a process called glycation. The higher your blood sugar runs, the more glucose sticks to hemoglobin. The A1C test measures the percentage of your hemoglobin that has glucose attached to it.
Red blood cells live an average of about 115 days, with a range of roughly 70 to 140 days. Because the test captures glucose that has been accumulating on hemoglobin throughout that lifespan, it reflects a weighted average of your blood sugar over roughly two to three months. More recent weeks count slightly more than earlier ones, since newer red blood cells are still circulating while older ones have been cleared.
The Three Diagnostic Ranges
The CDC uses these cutoffs for diagnosis:
- Below 5.7%: Normal blood sugar regulation. No further action needed beyond routine screening.
- 5.7% to 6.4%: Prediabetes. Blood sugar is higher than normal but not yet in the diabetes range. This is the window where lifestyle changes have the greatest impact on preventing progression.
- 6.5% or above: Diabetes. A second test is typically done to confirm the diagnosis unless symptoms are already present.
These thresholds apply to initial diagnosis. If you already have diabetes, your target will be set individually (more on that below).
Converting A1C to Average Blood Sugar
A percentage can feel abstract. One of the most useful ways to read your A1C is to convert it into an estimated average glucose (eAG), which tells you what your blood sugar has been running in the same units you’d see on a home glucose meter. The formula is straightforward: multiply your A1C by 28.7, then subtract 46.7. The result is in mg/dL.
Here’s what that looks like in practice:
- A1C of 5%: Average blood sugar around 97 mg/dL
- A1C of 6%: Average blood sugar around 126 mg/dL
- A1C of 7%: Average blood sugar around 154 mg/dL
- A1C of 8%: Average blood sugar around 183 mg/dL
- A1C of 9%: Average blood sugar around 212 mg/dL
- A1C of 10%: Average blood sugar around 240 mg/dL
Each full percentage point on the A1C scale corresponds to roughly a 29 mg/dL change in average blood sugar. So if your A1C drops from 8% to 7%, your daily average glucose has come down by about 29 mg/dL. That framing makes it easier to connect the lab number to what’s actually happening in your body day to day.
Keep in mind these are averages. An A1C of 7% could come from blood sugar that stays steady around 154 mg/dL, or from wide swings between highs and lows that happen to average out the same way. The A1C alone can’t distinguish between the two patterns.
What Your Target Should Be
For most adults with diabetes, the general treatment goal is an A1C below 7%. But this isn’t one-size-fits-all. A more relaxed target, such as below 8%, may be appropriate for older adults, people with a limited life expectancy, or anyone for whom aggressive blood sugar lowering carries more risk than benefit, like a higher chance of dangerous lows.
Younger, otherwise healthy people diagnosed early may aim for something tighter, closer to the normal range. Children and pregnant women have their own separate targets. The key point: if you’re managing diabetes, ask what your personal target is rather than assuming 7% is the universal goal.
How Often to Test
If your blood sugar is not yet at your target, testing every three months gives you and your care team enough data to adjust your plan. Once you’ve reached stable control, testing every six months is generally sufficient. More frequent testing may be recommended for children with type 1 diabetes, people planning pregnancy, or anyone who has recently made major medication or lifestyle changes.
Conditions That Skew Results
Because the A1C depends on red blood cell lifespan, anything that changes how long your red blood cells survive can push the number up or down independent of actual blood sugar levels. This is one of the most important things to understand when reading your results.
Conditions That Falsely Raise A1C
Iron deficiency anemia is the most common culprit. When your body doesn’t produce enough new red blood cells, existing cells circulate longer, accumulating more glucose on their hemoglobin. Vitamin B-12 and folate deficiency anemias have the same effect. People who have had their spleen removed also tend to get falsely elevated readings because red blood cells aren’t being cleared at the normal rate. Kidney disease with high urea levels can interfere with the test as well, creating a compound that some lab methods mistake for glycated hemoglobin. Chronic heavy alcohol use and long-term use of salicylates or opioids have also been linked to artificially higher readings.
Conditions That Falsely Lower A1C
Anything that shortens red blood cell lifespan works in the opposite direction. Significant blood loss, whether from surgery, heavy menstrual periods, or a bleeding disorder, means red blood cells haven’t been around long enough to accumulate a representative amount of glucose. Hemolytic anemias, where red blood cells break down prematurely, have the same effect. An enlarged spleen can clear red blood cells faster than normal. Pregnancy naturally shortens red blood cell lifespan from about 120 days to about 90 days and increases production of new cells, so A1C results during pregnancy tend to read lower than expected.
People with end-stage kidney disease often show falsely low readings, not because of the kidney failure itself, but because of the chronic anemia that accompanies it, which accelerates red blood cell turnover.
Hemoglobin variants, which are more common in people of African, Southeast Asian, or Mediterranean descent, can push A1C results in either direction depending on the specific lab method used. If you carry a hemoglobin trait like sickle cell trait, let your provider know so they can ensure the right testing method is used or order alternative tests like fructosamine.
Why Your A1C Might Change Unexpectedly
If your A1C shifts between tests and your eating habits haven’t changed, several other factors could explain it. Illness, infection, injury, or surgery trigger a stress response that raises blood sugar, sometimes for weeks. Emotional and physical stress do the same through the release of hormones that push glucose into the bloodstream. Hormonal changes from menstrual cycles or menopause can influence blood sugar patterns. Steroid medications are a particularly common cause of blood sugar spikes that show up on A1C results. Even inconsistent timing or dosing of diabetes medications can produce an unexpected change.
A single A1C reading is a snapshot of a three-month window. Looking at the trend across multiple tests gives a much clearer picture than fixating on any one number. A rise from 6.8% to 7.1% after a bout of pneumonia tells a different story than a steady climb from 6.5% to 7.0% to 7.5% over the course of a year.
How Labs Keep Results Accurate
A1C tests across different labs and different testing equipment are standardized through the National Glycohemoglobin Standardization Program (NGSP), which has been certifying manufacturers and laboratories since 1996. The program ensures that a result of 7.0% at one lab means the same thing at another. Labs are monitored monthly with blinded blood samples, and certified methods must stay within tight accuracy limits, no more than 0.35 percentage points of bias from the reference standard. This means you can generally trust that results from different labs or different visits are comparable, though point-of-care devices used in some clinics may have slightly more variability than full laboratory analyzers.