01 / Reference ranges
What counts as normal
Normal vs optimal
The ADA Standards do not print a "normal" row. They define prediabetes as 5.7 to 6.4% and describe glucose below that range as normoglycemia; the ADA's public diagnosis page states normal as less than 5.7%. Some clinics treat the low 5s as a better place to be than the high 5s. That reflects the continuous-risk language in the Standards, not a separate published threshold, so we do not print an "optimal" cutoff for A1C.
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02 / Why it matters
What the number tells you
A1C is one of the three tests the American Diabetes Association accepts to diagnose prediabetes and diabetes, and it does not require fasting. The ADA's 2026 Standards of Care set 6.5% or higher as diagnostic for diabetes and 5.7 to 6.4% as prediabetes, a range the ADA describes as identifying people at high risk for diabetes and cardiovascular outcomes. Risk is continuous: the ADA notes it extends below the lower limit of the prediabetes range and rises disproportionately at the top of it.
- For most nonpregnant adults who already have diabetes, the ADA's treatment goal is an A1C under 7%.
- A single reading is not a diagnosis. Diabetes is confirmed with a repeat test or a second abnormal test unless glucose is unmistakably high with symptoms.
03 / In practice
Testing and what moves it
When it is tested
- The USPSTF recommends screening adults 35 to 70 with overweight or obesity for prediabetes and type 2 diabetes, repeating about every 3 years if normal.
- People with diabetes are typically tested every 3 to 6 months to track treatment.
- The lab method must be NGSP-certified and standardized to the DCCT assay for the diagnostic cutoffs to apply.
What raises it
- Sustained high blood glucose from insulin resistance or insufficient insulin.
- Conditions that lengthen red-cell lifespan (for example iron deficiency anemia can raise A1C for a given glucose).
What lowers it
- Lower average glucose: weight loss, higher activity, dietary change, glucose-lowering medication.
- Conditions that shorten red-cell lifespan or increase turnover (hemolysis, recent blood loss, some hemoglobin variants) can read falsely low; the ADA advises glucose criteria in those cases.
04 / Related
Read next
Frequently asked questions
Do I need to fast for an A1C test? ▼
No. A1C reflects average glucose over roughly three months, so the ADA accepts it without fasting. Fasting glucose and the oral glucose tolerance test do require fasting.
Is 5.7% prediabetes or normal? ▼
Under the ADA Standards of Care 2026, 5.7% is the bottom of the prediabetes range (5.7 to 6.4%). The ADA also notes risk is continuous, so 5.6% is not risk-free and 5.7% is not a diagnosis of diabetes.
Can an at-home A1C test diagnose diabetes? ▼
Diagnosis requires a laboratory method that is NGSP-certified and standardized to the DCCT assay, and usually a confirmatory test. At-home kits that send a dried blood spot to a certified lab can meet the assay standard, but a clinician still needs to confirm and act on the result.