HbA1c: A Beginner-Friendly Start
HbA1c: the few things that matter most, and the mistakes that catch people out early.
A blood test, often called the A1C, reflecting average blood glucose over the preceding two to three months.
Key takeaways
- What it reflects: average glucose over 2-3 months
- Diagnostic threshold: 6.5% or above
- Most useful single change: Ask what your number is and what your target is.
- Commonest mistake: Judging control on a single reading in isolation.
- See a doctor if any of the signs under "When to speak to a doctor" below apply to you.
Why bother
It needs no fasting and smooths out daily variation, which makes it one of the standard tests for diagnosis and monitoring.
Start here
Two things, and nothing else until both feel routine.
- Ask what your number is and what your target is
- Understand it is an average; it hides day-to-day swings
Then add these
Once the first two are automatic, these are worth adding.
- Have it rechecked at the interval your care team advises, often every 3 to 6 months
- Mention sickle cell trait, thalassemia or a recent transfusion, which affect accuracy
The numbers, in one place
| Measure | Figure |
|---|---|
| What it reflects | average glucose over 2-3 months |
| Diagnostic threshold | 6.5% or above |
| Prediabetes range | 5.7% to 6.4% |
| Common target for many adults with diabetes | below 7%, set individually with your care team |
| Less reliable in | hemoglobin variants, pregnancy, recent blood loss or transfusion, advanced kidney disease |
Common early mistakes
- Judging control on a single reading in isolation
- Assuming a good A1C means no low blood sugar is occurring
- Chasing a very low target if you are frail or prone to lows
Related topics
- Blood Tests Explained: Sorting the Evidence From the Noise (Blood Health)
- Having a Blood Test: Sorting the Evidence From the Noise (Using Health Services)
- What the Guidance Really Says About Blood Pressure Checks (Preventive Care)
- What the Guidance Really Says About Diabetes and the Kidneys (Kidney Health)
Where to go next
- Your Questions About HbA1c, Answered
- HbA1c in Five Minutes
- HbA1c — the reference entry
- Diabetes: The Complete Guide
- The Evidence on Diabetic Foot Care, Without the Hype
- Hypoglycemia: What Published Guidance Supports
When to speak to a doctor
Call 911 for symptoms of very high glucose with vomiting, abdominal pain, deep breathing or drowsiness. If you take insulin or a sulfonylurea, treat low blood sugar immediately with fast-acting carbohydrate, call 911 for any loss of consciousness, and see your doctor about repeated episodes.
Where this comes from
- National Institute of Diabetes and Digestive and Kidney Diseases — The A1C Test & Diabetes
- American Diabetes Association — Standards of Care in Diabetes
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.
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