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Early detection

HbA1c: a record written in red blood cells

Learn what glycated hemoglobin measures, why it reflects recent glucose exposure, and when its interpretation can be misleading.

2 min readEasy read2 sourcesChecked 30 Sept 2026Established

By The Diabetes Guide editorial project · Updated 30 Sept 2026

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In simple words

HbA1c is a blood test that shows your average sugar over the last few months. Sugar sticks to a protein in red blood cells, and the test measures how much has stuck.

  1. Step 1: A sugar diary in your blood

    The more sugar in the blood over time, the more sticks to hemoglobin.

    For example: Like a photograph with a long exposure that shows the whole trail of a moving light.

  2. Step 2: The ranges

    Below 5.7% is under the prediabetes range, 5.7–6.4% is prediabetes and 6.5% or more is the diabetes range.

    For example: Green, yellow and red on a traffic light.

  3. Step 3: When it can mislead

    Blood loss, some anemias and kidney disease can make the result look higher or lower than the real sugar.

    For example: A ruler that has shrunk gives wrong answers even if you read it correctly.

Remember: No fasting needed, but anemia and some blood conditions can change the result.

The full story

Want more? Below is the detailed version with the real science words. It is fine to skip it.

What it measures

Hemoglobin carries oxygen inside red blood cells. Glucose attaches to it through glycation, a nonenzymatic chemical process. HbA1c measures the glycated fraction and reflects recent months of glucose exposure, weighted more toward recent weeks. It is not a direct recording of every glucose value. 1

Ranges and advantages

For nonpregnant people using ADA criteria, below 5.7% is below the prediabetes range, 5.7–6.4% indicates prediabetes, and at least 6.5% is diabetes range. A suitable standardized assay is required. Fasting is unnecessary; a single sample is convenient. 2

Limitations and misleading results

Anemia, blood loss, transfusion, hemolysis, kidney disease and some hemoglobin variants can alter interpretation. Shortened red-cell survival may lower HbA1c relative to glucose; other disturbances can raise it. A1c can miss rapidly developing hyperglycemia and does not show glycemic variability. If it conflicts with plasma glucose, clinicians investigate and may use glucose-based criteria.

Trace the evidence

Sources and further reading

1.The A1C Test & Diabetes (opens in a new tab)

NIH / NIDDK · 2026 · Reference

Established
Who was studied, limits and source check

Limitations: Living reference accessed in 2026; red-cell disorders can make A1c unreliable.

Source checked 2026-09-30. See the original publication for full methods.

2.Diabetes Tests & Diagnosis (opens in a new tab)

NIH / NIDDK · 2026 · Reference

Established
Who was studied, limits and source check

Limitations: Living patient resource; year denotes access year, not a newly published study.

Source checked 2026-09-30. See the original publication for full methods.

Source checking is an editorial literature check, not independent medical review. This page is for learning. It cannot diagnose you or make a treatment plan. Evidence labels describe the cited claims, not the whole topic.

What does “Established” mean?

Doctors and scientists agree. This is well known. Like “the sun rises in the east”.

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