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Lab test explainer

A1C

A1C reflects average blood glucose over about the past three months. It does not show short-term highs and lows.

Printed on reports as: HbA1c · Hemoglobin A1c · Glycated hemoglobin · A1C

What it measures

The percentage of hemoglobin with glucose attached. It reflects average blood glucose over roughly the previous three months, with the most recent 30 days contributing more to the result than earlier months.

Why it is checked

Clinicians use it in defined settings to help screen for or diagnose prediabetes or type 2 diabetes, and to monitor diabetes over time. It does not require fasting.

What can affect the result
  • Changes in red blood cell lifespan, including recent blood loss, sickle cell disease, erythropoietin treatment, hemodialysis or transfusion, can change A1C.
  • Very low iron (such as iron-deficiency anemia) can falsely raise results. Kidney failure and liver disease can also cause false results.
  • Hemoglobin variants can make some A1C methods unreliable for diagnosing or monitoring diabetes. Some test types still suit specific variants, so ask the laboratory which method was used.
Read alongside

Blood glucose measures a moment in time. If glucose results and A1C disagree, a clinician can assess whether timing, changes over time, or an influence on A1C explains the difference.

Peptide connections

No prescribing-information instruction on this page names A1C. A human study of a glucose-lowering medicine may measure A1C as an outcome of glucose control. That is a study purpose, separate from any monitoring instruction.

This page cites no prescribing-information or guideline connection for A1C. See all peptide connections →

A connection describes what a source says about monitoring. It does not show that a result makes anyone eligible for, or a candidate for, a medication.

Questions for your healthcare team

“Does my A1C fit my other glucose results, and is there anything that could make it less reliable for me?”

Add it to the appointment worksheet →

Sources and review status

  • The NIDDK page was last reviewed in April 2018 and its references are older; current guidance may differ. Diagnostic thresholds are shown on the page text only as context and need clinician or guideline confirmation before publication.
  • No human-study example is cited yet. A study-based A1C connection should be added only after a specific trial, product and population are verified.

General education only. Bring your report, symptoms, and medication list to a qualified healthcare professional for advice about your care. Follow instructions from your lab or clinician if a result is marked critical.