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What does a high HbA1c mean?

Updated October 31, 2026 · 16 sources · Written by the AumniVIDA team

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Short answer

A high HbA1c means more hemoglobin has glucose attached, usually because average glucose has been raised for months. ADA calls 5.7 to 6.4% (39 to 47 mmol/mol)39 to 47 mmol/mol (5.7 to 6.4%) prediabetes and 6.5% (48 mmol/mol)48 mmol/mol (6.5%) or higher the diabetes range. A diagnosis needs a second test, and iron deficiency can raise HbA1c without high glucose .

Future diabetes risk by baseline HbA1c in adults without diabetes

Show the data
Future diabetes risk by baseline HbA1c in adults without diabetes
ItemValue (hazard ratio for diagnosed diabetes)LowHighNote
Below 5.0%0.520.40.69
5.0 to 5.4% (reference)1
5.5 to 5.9%1.861.672.08
6.0 to 6.4%4.483.925.13
6.5% or higher16.4714.2219.08
In the ARIC study, risk of diagnosed diabetes rose steadily with HbA1c: 1.9 times at 5.5 to 5.9% and 4.5 times at 6.0 to 6.4%, compared with 5.0 to 5.4%.

Key takeaways

  1. 1

    5.7 to 6.4% (39 to 47 mmol/mol)39 to 47 mmol/mol (5.7 to 6.4%) is prediabetes by ADA criteria; 6.5% (48 mmol/mol)48 mmol/mol (6.5%) or higher is in the diabetes range [1].

  2. 2

    Diagnosis needs two abnormal results unless symptoms are clear [1].

  3. 3

    In ARIC, 6.0 to 6.4% carried 4.48 times the diabetes risk of 5.0 to 5.4% [3].

  4. 4

    A high A1c with normal glucose can reflect iron deficiency, red cell lifespan or ancestry, or glucose that is high after meals but normal when fasting [2] [4].

  5. 5

    Lifestyle change cut progression from prediabetes to diabetes by 58% in the Diabetes Prevention Program [5].

What does a high A1c mean?

A high A1c usually means average glucose has been raised over the past 2 to 3 months. Under ADA criteria, 5.7 to 6.4% (39 to 47 mmol/mol)39 to 47 mmol/mol (5.7 to 6.4%) is prediabetes and 6.5% (48 mmol/mol)48 mmol/mol (6.5%) or higher is the diabetes range [1].

The higher the number, the stronger the link to complications. In type 2 diabetes, each 1 point higher A1c was associated with 37% more microvascular complications and 14% more heart attacks [6]. Below the diabetes range, risk of future diabetes and heart disease rises from about 5.5% [3].

A high A1c alone rarely causes symptoms. Symptoms such as thirst, frequent urination and weight loss come from very high glucose, not from A1c itself [1].

What does an A1c of 5.7 mean?

An A1c of 5.7% (39 mmol/mol)39 mmol/mol (5.7%) is the lower edge of the ADA prediabetes range. It signals raised risk of type 2 diabetes, and ADA advises testing again every year [1]. NICE starts its high-risk range higher, at 6.0% (42 mmol/mol)42 mmol/mol (6.0%) [7].

Prediabetes is a risk state, not a disease. In ARIC, people at 5.5 to 5.9% had 1.86 times the risk of developing diabetes over the following years, and people at 6.0 to 6.4% had 4.48 times the risk, compared with 5.0 to 5.4% [3].

Risk can be lowered. In the Diabetes Prevention Program, a lifestyle program aiming at 7% weight loss and 150 minutes of activity a week cut new diabetes by 58% over 2.8 years [5]. See how to lower HbA1c for the levers and their effect sizes.

Future diabetes risk by baseline HbA1c in adults without diabetes

Show the data
Future diabetes risk by baseline HbA1c in adults without diabetes
ItemValue (hazard ratio for diagnosed diabetes)LowHighNote
Below 5.0%0.520.40.69
5.0 to 5.4% (reference)1
5.5 to 5.9%1.861.672.08
6.0 to 6.4%4.483.925.13
6.5% or higher16.4714.2219.08
In the ARIC study, risk of diagnosed diabetes rose steadily with HbA1c: 1.9 times at 5.5 to 5.9% and 4.5 times at 6.0 to 6.4%, compared with 5.0 to 5.4%.

What A1c is the cutoff for diabetes?

The cutoff is 6.5% (48 mmol/mol)48 mmol/mol (6.5%) under ADA, WHO, NICE and the International Expert Committee. It was set where moderate retinopathy becomes clearly more common, and it needs confirmation by a second abnormal result [1] [8] [9].

ADA's example: an A1c of 7.0% (53 mmol/mol)53 mmol/mol (7.0%) followed by a repeat of 6.8% (51 mmol/mol)51 mmol/mol (6.8%) confirms diabetes. Two different tests from the same sample also count, for example A1c and fasting glucose. If A1c is in the diabetes range on two tests but fasting glucose is below 126 mg/dL (7.0 mmol/L)7.0 mmol/L (126 mg/dL), the person is still considered to have diabetes [1].

WHO adds that an A1c below 6.5% does not rule out diabetes diagnosed by glucose tests [8]. The cut point is a line drawn on a continuum, not a biological switch [9].

Why is my A1c high when my glucose is normal?

Fasting glucose captures one moment before breakfast, while A1c reflects glucose around the clock, including after meals, so the two can disagree. A1c can also read high from iron deficiency, long-lived red cells, kidney failure or ancestry differences rather than high glucose [2] [4] [1].

Common reasons for a high A1c with normal fasting glucose:

  • Glucose that rises after meals. Some people keep normal fasting glucose but spend hours higher after eating. A1c picks this up; a fasting test does not.
  • Iron deficiency. It raises A1c with no rise in glucose [2]. Check ferritin.
  • Red cells that live longer. Mean red cell age varies widely even in healthy people, and older cells carry more glucose [4]. Splenectomy, which changes red cell turnover, is also on ADA's list [1].
  • Ancestry and age. A1c runs 0.24 to 0.26 points higher in Asian and Black people than in White people at similar glucose [10], and rises with age [11].
  • Lab interference. Some assays are affected by hemoglobin variants [1].

ADA recommends looking for an analytical problem or interference whenever A1c and glucose are consistently and substantially out of step [1]. An oral glucose tolerance test, fructosamine or a period of CGM can settle which measure reflects your glucose [12] [13]. The reverse also happens: anemia, blood loss, sickle cell trait or G6PD deficiency can make A1c read low when glucose is high [14] [1].

Minimal illustration of two round dial gauges side by side, their needles pointing to different positions.
A glucose reading is a snapshot of one moment; HbA1c is a weighted summary of months, so the two can point in different directions.

What causes a high A1c besides diabetes?

Besides raised glucose, A1c can read high with iron deficiency, long-lived red cells, kidney failure, some hemoglobin variants depending on the assay, older age and ancestry. ADA lists these as factors that alter the link between A1c and glucose [1] [2].

Most high A1c results do reflect higher glucose. The factors above matter most near a threshold, where a shift of 0.2 to 0.3 points can move a result between categories [10] [14]. Your clinician can check iron status and blood count and choose a different test if needed [1].

What should you do after a high A1c result?

Confirm it. ADA requires a second abnormal result before diagnosing diabetes, and advises yearly testing for anyone in the prediabetes range [1]. Talk to a clinician about the result, any factors that might distort it, and a plan.

Useful steps to discuss:

AumniVIDA explains results for general wellness and does not diagnose. A clinician makes the diagnosis.

More about HbA1c

Protocols that act on HbA1c

Common questions

Is an A1c of 6.0 prediabetes?

Yes. 6.0% (42 mmol/mol)42 mmol/mol (6.0%) is in the ADA prediabetes range and at the start of NICE's high-risk range [1] [7].

Can A1c be falsely elevated?

Yes. Iron deficiency, long-lived red cells, kidney failure and some assay interferences can raise A1c without raised glucose [2] [1].

Does a high A1c cause symptoms?

Usually not by itself. Prediabetes and early diabetes often have no symptoms; thirst, frequent urination and weight loss come with very high glucose [1].

Is a high A1c reversible?

Often. In DiRECT, 46% of people with type 2 diabetes reached an A1c below 6.5% without medication after a structured weight loss program [15], and in PLIS 43% of people with prediabetes who lost 5% of their weight returned to normal [16].

Can A1c be high but blood sugar low?

Yes. If finger-prick readings are taken mostly when fasting, they miss after-meal rises; and red cell factors such as iron deficiency can raise A1c on their own [2]. A period of CGM shows the full day [13].

Sources

  1. 1.American Diabetes Association Professional Practice Committee for Diabetes. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes-2026. Diabetes Care, 2026. doi:10.2337/dc26-S002
  2. 2.English E, Idris I, Smith G, Dhatariya K, Kilpatrick ES, John WG. The effect of anaemia and abnormalities of erythrocyte indices on HbA1c analysis: a systematic review. Diabetologia, 2015. doi:10.1007/s00125-015-3599-3
  3. 3.Selvin E, Steffes MW, Zhu H, et al. Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults. New England Journal of Medicine, 2010. doi:10.1056/NEJMoa0908359
  4. 4.Cohen RM, Franco RS, Khera PK, et al. Red cell life span heterogeneity in hematologically normal people is sufficient to alter HbA1c. Blood, 2008. doi:10.1182/blood-2008-04-154112
  5. 5.Knowler WC, Barrett-Connor E, Fowler SE, et al. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. New England Journal of Medicine, 2002. doi:10.1056/NEJMoa012512
  6. 6.Stratton IM, Adler AI, Neil HA, et al. Association of glycaemia with macrovascular and microvascular complications of type 2 diabetes (UKPDS 35): prospective observational study. BMJ, 2000. doi:10.1136/bmj.321.7258.405
  7. 7.National Institute for Health and Care Excellence. Type 2 diabetes: prevention in people at high risk (PH38). NICE public health guideline, 2012. Link
  8. 8.World Health Organization. Use of glycated haemoglobin (HbA1c) in diagnosis of diabetes mellitus: abbreviated report of a WHO consultation. World Health Organization, 2011. Link
  9. 9.International Expert Committee. International Expert Committee report on the role of the A1C assay in the diagnosis of diabetes. Diabetes Care, 2009. doi:10.2337/dc09-9033
  10. 10.Cavagnolli G, Pimentel AL, Freitas PA, Gross JL, Camargo JL. Effect of ethnicity on HbA1c levels in individuals without diabetes: Systematic review and meta-analysis. PLoS One, 2017. doi:10.1371/journal.pone.0171315
  11. 11.Pani LN, Korenda L, Meigs JB, et al. Effect of aging on A1C levels in individuals without diabetes: evidence from the Framingham Offspring Study and the National Health and Nutrition Examination Survey 2001-2004. Diabetes Care, 2008. doi:10.2337/dc08-0577
  12. 12.American Diabetes Association Professional Practice Committee for Diabetes. 6. Glycemic Goals, Hypoglycemia, and Hyperglycemic Crises: Standards of Care in Diabetes-2026. Diabetes Care, 2026. doi:10.2337/dc26-S006
  13. 13.Battelino T, Danne T, Bergenstal RM, et al. Clinical Targets for Continuous Glucose Monitoring Data Interpretation: Recommendations From the International Consensus on Time in Range. Diabetes Care, 2019. doi:10.2337/dci19-0028
  14. 14.Lacy ME, Wellenius GA, Sumner AE, et al. Association of Sickle Cell Trait With Hemoglobin A1c in African Americans. JAMA, 2017. doi:10.1001/jama.2016.21035
  15. 15.Lean ME, Leslie WS, Barnes AC, et al. Primary care-led weight management for remission of type 2 diabetes (DiRECT): an open-label, cluster-randomised trial. Lancet, 2018. doi:10.1016/S0140-6736(17)33102-1
  16. 16.Sandforth A, von Schwartzenberg RJ, Arreola EV, et al. Mechanisms of weight loss-induced remission in people with prediabetes: a post-hoc analysis of the randomised, controlled, multicentre Prediabetes Lifestyle Intervention Study (PLIS). Lancet Diabetes and Endocrinology, 2023. doi:10.1016/S2213-8587(23)00235-8

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