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Diabetes screening

A1C and blood sugar test results: what they mean

An A1C below 5.7%, or a fasting blood sugar below 100 mg/dL, is in the normal range; higher numbers can mean prediabetes or diabetes. A single high result is usually confirmed with a second test before diabetes is diagnosed. Your doctor reads your results with your health history and decides what comes next. (ADA, 2026) (NIDDK, 2022)

The ranges, by test

These are the American Diabetes Association cut points for people who are not pregnant. For all three main tests, risk rises steadily across the range and climbs faster at the top of it. (ADA, 2026) In pregnancy some tests use different cutoffs, so ask your doctor what your numbers mean. (NIDDK, 2022)

A1C and plasma glucose ranges for normal, prediabetes and diabetes in people who are not pregnant, ADA Standards of Care 2026
TestNormalPrediabetesDiabetes range
A1CBelow 5.7%5.7% to 6.4% (39 to 47 mmol/mol)6.5% or higher (48 mmol/mol or higher) (ADA, 2026)
Fasting plasma glucoseBelow 100 mg/dL100 to 125 mg/dL (5.6 to 6.9 mmol/L)126 mg/dL or higher (7.0 mmol/L or higher) (ADA, 2026)
2-hour glucose tolerance test (75 g)Below 140 mg/dL140 to 199 mg/dL (7.8 to 11.0 mmol/L)200 mg/dL or higher (11.1 mmol/L or higher) (ADA, 2026)
Random plasma glucose, with classic symptomsNot used for thisNot used for this200 mg/dL or higher (11.1 mmol/L or higher) (ADA, 2026)

What each test measures

  • A1C (also called hemoglobin A1C or HbA1c): your average blood sugar over about the last 3 months. You can eat and drink before it. (NIDDK, 2022) It is weighted toward recent weeks, and it changes less with day-to-day stress, food or illness than glucose tests do. (ADA, 2026)
  • Fasting plasma glucose: your blood sugar at one point in time, usually in the morning after at least 8 hours with nothing to eat or drink except sips of water. (NIDDK, 2022)
  • Oral glucose tolerance test (OGTT): after at least 8 hours of fasting, blood is drawn, you drink a sugary liquid, and blood is drawn again 2 hours later. (NIDDK, 2022) The ADA says the 2-hour result finds more people with prediabetes and diabetes than the A1C or fasting cut points do. (ADA, 2026)
  • Random plasma glucose: taken at any time of day. It is used when someone has symptoms of diabetes and the doctor does not want to wait for a fasting test. (NIDDK, 2022)

The three main tests measure different things and do not always pick out the same people. (ADA, 2026)

Why a second test confirms diabetes

Unless blood sugar is clearly very high, for example a random glucose of 200 mg/dL or more with classic symptoms such as thirst, passing a lot of urine and unexplained weight loss, the ADA says a diabetes diagnosis needs two abnormal results. That can be the same test repeated on another day, or two different tests, such as A1C and fasting glucose, taken at the same time or on different days. The second test should be done in a timely way. (ADA, 2026)

  • If two different tests disagree, the one above the cut point is repeated. (ADA, 2026)
  • Results close to a cut point should lead to a repeat test in 3 to 6 months, and to learning the symptoms of high blood sugar. (ADA, 2026)
  • The USPSTF also says a type 2 diabetes diagnosis should be confirmed with repeat testing. (USPSTF, 2021)

What can make an A1C misleading

A1C depends on red blood cells, so anything that changes them can change the result. The ADA lists:

  • anemia, iron levels, blood loss, a transfusion, removal of the spleen, faster breakdown of red blood cells, or treatment with erythropoietin;
  • kidney failure and dialysis, cirrhosis, HIV and some HIV treatment, and pregnancy;
  • some hemoglobin variants, such as sickle cell trait, which need an A1C method that is not affected by them;
  • G6PD deficiency: one common variant, carried by about 11% of Black people in the US, can lower A1C by about 0.7% to 0.8%. (ADA, 2026)

In these situations the ADA says glucose tests should be used for the diagnosis instead. (ADA, 2026) The ADA also notes that studies found slightly higher A1C levels, about 0.3%, in Black adults than in non-Hispanic White or Hispanic adults, that this is debated, and that the link between A1C and the risk of complications appears similar across these groups; it says race should not be used as a stand-in for poorly understood genetic differences. (ADA, 2026)

What usually comes next

  • Normal: the USPSTF says the best interval is uncertain and that testing every 3 years may be reasonable. (USPSTF, 2021)
  • Prediabetes: the USPSTF says clinicians should offer or refer people with prediabetes to effective preventive interventions, and that lifestyle programs focused on diet, physical activity or both have been shown to prevent or delay diabetes. (USPSTF, 2021) The ADA advises a test every year. (ADA, 2026)
  • Diabetes range: a second test to confirm it, as above, and then a plan made with your doctor. Regular checks for people who have diabetes are on screenings if you have diabetes.

Who should be screened, and from what age, is on diabetes screening.

What Medicare covers

Medicare Part B covers up to 2 diabetes screening tests a year for people with risk factors such as high blood pressure, abnormal cholesterol and triglyceride levels, obesity or a past high blood sugar. The tests can be fasting or non-fasting glucose tests or A1C tests, and you pay nothing if your provider accepts assignment. (Medicare.gov)

Questions people ask

What is a normal A1C?

Below 5.7%. An A1C of 5.7% to 6.4% is in the prediabetes range and 6.5% or higher is in the diabetes range, for people who are not pregnant. Risk rises steadily across the range rather than starting at one number. (ADA, 2026)

Does one high A1C mean I have diabetes?

Not on its own, unless blood sugar is clearly very high with symptoms. The ADA says the diagnosis needs two abnormal results: the same test repeated, or two different tests, such as A1C and fasting glucose, taken at the same time or on different days. (ADA, 2026)

Do I need to fast for an A1C test?

No. You can eat and drink before an A1C test. A fasting plasma glucose test and a glucose tolerance test need at least 8 hours with nothing to eat or drink except sips of water. (NIDDK, 2022)

My A1C and fasting glucose disagree. Which one counts?

The ADA says the result that is above the diagnostic cut point should be repeated, taking into account anything that can affect A1C or glucose. If the two tests keep disagreeing, your doctor looks for the reason. (ADA, 2026)

What happens if I have prediabetes?

The USPSTF says clinicians should offer or refer people with prediabetes to effective preventive interventions; lifestyle programs focused on diet, physical activity or both have been shown to prevent or delay diabetes. The ADA says to test every year. Your doctor decides what fits you. (USPSTF, 2021) (ADA, 2026)

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