Hemoglobin A1C
Also written as: HbA1c, Glycated hemoglobin
An average of your blood sugar over roughly the past three months.
What it measures
The percentage of hemoglobin with glucose attached to it. Because red cells live around three months, it reflects average blood sugar across that window rather than at one moment.
Why a doctor orders it
Used to screen for and diagnose diabetes and prediabetes, and to monitor blood sugar control over time without requiring fasting.
What is generally associated with a higher result
A higher A1C reflects higher average blood sugar over the period. It can also be raised by conditions that lengthen red cell lifespan, including iron deficiency anemia.
What is generally associated with a lower result
A lower A1C reflects lower average blood sugar, but can also be produced by anything that shortens red cell lifespan - recent blood loss, hemolysis, some hemoglobin variants, recent transfusion, and pregnancy.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- Any condition affecting red blood cell lifespan
- Hemoglobin variants, which affect some assay methods
- Recent transfusion
- Pregnancy
Questions to take to your appointment
- Does anything about my red blood cells make this less reliable for me?
- How does this compare with my home glucose readings?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
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