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Hemoglobin A1C (HbA1c)
The share of hemoglobin coated with glucose — an average picture of blood sugar over the past two to three months.
Other names: A1C, glycated hemoglobin, glycohemoglobinSection: Blood chemistry
Updated: August 29, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortA1C shows average blood glucose over two to three months. Below 5.7% (below 39 mmol/mol) is normal, 5.7–6.4% (39–46 mmol/mol) is the prediabetes range, and 6.5% (48 mmol/mol) or higher meets the diabetes threshold. No fasting is needed, and a result above the range is usually confirmed with a second test.
Reference ranges
Group
Reference range
Normal
below 5.7% (below 39 mmol/mol)
Prediabetes
5.7–6.4% (39–46 mmol/mol)
Diabetes
6.5% or higher (48 mmol/mol or higher)
These ranges come from the MedlinePlus medical test page and are a general guide: what is normal for a specific person depends on health, age, and other factors, and the provider's interpretation applies. Reference ranges vary between laboratories and assays — use the range printed on your own lab report. Values in mmol/mol are the IFCC units, recalculated from the percentage.
Reference range vs optimal — not the same thing
Normal is below 5.7% (<39 mmol/mol). Metabolically healthy people typically run 4.8–5.4%. Conversion: mmol/mol = 10.93 × % − 23.5.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
Glucose in the bloodstream sticks to hemoglobin, the protein inside red blood cells. The higher the blood glucose over time, the more hemoglobin ends up coated. An A1C test measures the percentage of hemoglobin that carries this glucose coating.
Because red blood cells live for about three months, that percentage works out as an average of blood sugar over the past two to three months. A home glucose meter, by contrast, only ever shows the level at the moment of the measurement — the two complement each other rather than replace each other.
The test is used to screen for prediabetes and type 2 diabetes and to monitor how well blood glucose has been controlled over time. Most people with diabetes have an A1C test at least twice a year. It is not used to diagnose type 1 diabetes, though it can still help with monitoring once type 1 is established.
Prediabetes deserves a special note: blood sugar is higher than normal but not yet in the diabetes range, and lifestyle changes at this stage — healthier eating and regular movement — can delay or prevent type 2 diabetes. An A1C is often how prediabetes is first spotted.
When it is high
PrediabetesAn A1C between 5.7% and 6.4% (39–46 mmol/mol) means average blood sugar is above normal but below the diabetes line.
DiabetesAn A1C of 6.5% (48 mmol/mol) or higher meets the diagnostic threshold; providers generally use more than one test to confirm the diagnosis.
Poorly controlled known diabetesIn someone already diagnosed, a rising A1C means average glucose has been running high over the past months, which over time raises the risk of heart, kidney, and nerve damage.
When it is low
Not applicable in the usual senseA1C does not have a 'too low' clinical problem in general use. Certain medicines such as opioids and some HIV medicines can affect the result, so the provider is usually told about everything being taken — without stopping anything on one's own. Pregnancy can also change how the result is read.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Opioids and some HIV medicinesPregnancyRecent changes in glucose control
How to prepare
No fasting and no special preparation are needed: the test works at any time of day regardless of meals. That convenience is one reason it is used so widely for screening.
When a retest makes sense
A result above the normal range is typically confirmed — with a repeat A1C or a different diabetes test such as a fasting glucose or an OGTT. For people with diabetes, the described routine is an A1C at least twice a year to track control over time.
Who usually reviews this result
A result outside the reference range is usually reviewed by: your GP or primary care doctor; an endocrinologist for diabetes care. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: HbA1cA1CGlycated hemoglobinGlycosylated hemoglobinGlycohemoglobin
No. They answer different questions: the meter shows the level at one moment, A1C shows the average across two to three months. Day-to-day management relies on moment readings; long-term control is judged by A1C.
How often is an A1C test done?
For people with diabetes, MedlinePlus describes at least twice a year as the usual routine. For screening without risk factors, the cadence is set by the provider based on age and risk profile.
Can A1C diagnose type 1 diabetes?
It is not used to diagnose type 1 diabetes, which usually announces itself quickly and is confirmed in other ways. A1C can still be part of monitoring once type 1 diabetes is established.
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