HbA1c and prediabetes: how to read your blood sugar results
Medically Reviewed by Dr. Pedro Yelamo Vera, MD
Licensed Physician No. 484814280 · Official Medical College of Bizkaia (Spain)Last reviewed: 12 October 2026
HbA1c explained: what it measures, % and mmol/mol, why ADA and WHO/Spanish cut-offs differ, when results mislead, and when a test must be repeated.
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HbA1c is one of the most common blood tests in diabetes care. If you live in Spain, your report may show it in two units and use cut-offs that differ from what you saw at home. This guide explains what the numbers mean, why experts draw the lines in slightly different places, and when a result needs a second look.
- HbA1c shows your average blood sugar over roughly the past three months. You do not need to fast for it.
- An HbA1c of 6.5% (48 mmol/mol) or more is in the diabetes range. Most people need a second test to confirm it.
- The ADA calls 5.7–6.4% (39–47 mmol/mol) prediabetes. Spanish practice, following WHO-based criteria, often uses 6.0–6.4% (42–47 mmol/mol).
- Anaemia, some inherited haemoglobin types, pregnancy, blood loss or a recent transfusion can make HbA1c wrong.
Dr. Pedro Yelamo Vera is a GP licensed in Spain (Colegiado No. 484814280).
For a medical emergency, call 112 or go to the nearest local emergency department. Do not wait for a video consultation or an online reply.
What HbA1c measures
Haemoglobin is the protein in red blood cells that carries oxygen. Sugar in your blood sticks to it. The higher your blood sugar, the more haemoglobin ends up with sugar attached.
Red blood cells live for about three months. So HbA1c shows your average blood sugar over that time, not just on the day of the test. In Spain it is often called hemoglobina glicosilada or glicada.
This makes it useful in two ways:
- To help diagnose diabetes or a higher risk of it.
- To follow how well diabetes is controlled over time.
You do not need to fast. One meal will not change it much.
Two units: % and mmol/mol
Labs report HbA1c in one or both of two units. Many Spanish reports show both.
- Percent (%), used in the US and many other places.
- mmol/mol, an international unit used in the UK and across much of Europe.
They describe the same thing. Here are the key points side by side:
| HbA1c (%) | HbA1c (mmol/mol) | What this level is used for |
|---|---|---|
| 5.7% | 39 | Lower edge of the ADA prediabetes range |
| 6.0% | 42 | Lower edge of the higher-risk range used in Spain and the UK |
| 6.4% | 47 (upper limit) | Top of the higher-risk range in all systems |
| 6.5% | 48 | Diabetes cut-off (ADA and WHO) |
These are diagnostic cut-offs. Treatment targets for people who already have diabetes are set one by one with the doctor.
Diabetes and prediabetes cut-offs
Experts agree on the diabetes line. They differ on where "higher risk" starts.
The diabetes range
The ADA and the WHO both use an HbA1c of 6.5% (48 mmol/mol) or more. The WHO adds that the lab must use a standard, quality-checked method.
A value under 6.5% does not rule diabetes out. A glucose test can still show it.
Prediabetes: why the lines differ
Prediabetes means blood sugar is above normal but below the diabetes range. It raises the risk of type 2 diabetes and heart disease.
| Test | ADA (US) | WHO-based criteria (Spanish Diabetes Society) | Diabetes range |
|---|---|---|---|
| HbA1c | 5.7–6.4% (39–47 mmol/mol) | 6.0–6.4% (42–47 mmol/mol) | 6.5% (48 mmol/mol) or more |
| Fasting glucose | 100–125 mg/dL (5.6–6.9 mmol/L) | 110–125 mg/dL (6.1–6.9 mmol/L) | 126 mg/dL (7.0 mmol/L) or more |
| 2-hour glucose (OGTT) | 140–199 mg/dL (7.8–11.0 mmol/L) | 140–199 mg/dL (7.8–11.0 mmol/L) | 200 mg/dL (11.1 mmol/L) or more |
So the same result can be read in two ways. An HbA1c of 5.8% is prediabetes by ADA rules. In Spain it is often seen as normal or borderline. Neither view is "wrong". They reflect different choices about how early to flag risk.
The WHO itself has not set a formal HbA1c range for this middle zone. It said the evidence was not strong enough.
If your report came from another country, check which rules it used. Your GP in Spain will usually apply Spanish practice.
Fasting glucose and the glucose tolerance test
HbA1c is not the only test. Two others measure sugar in a single blood sample.
- Fasting plasma glucose. A blood test after at least eight hours with no food. Spanish labs report it in mg/dL.
- Oral glucose tolerance test (OGTT). You drink a set amount of sugar in water. Blood is taken two hours later. It is used when other tests disagree, and in pregnancy.
The three tests do not always pick out the same people. Your fasting glucose can be normal while your HbA1c is raised, or the other way round.
When HbA1c can mislead
HbA1c depends on how long your red blood cells live. Anything that changes that can push the result up or down. Tell your doctor if any of these apply:
- Anaemia, such as low iron or B12, or anaemia from blood breaking down.
- Haemoglobin variants, such as sickle cell trait or thalassaemia. Some lab methods handle these better than others.
- Pregnancy. Red cells turn over faster, so glucose tests are preferred.
- Recent blood loss or a blood transfusion.
- Kidney failure or serious liver disease.
- Some medicines, including some used for HIV.
In these cases, your doctor may rely on glucose tests instead.
Anaemia is common and easy to miss. If your full blood count shows low haemoglobin, read our guide to full blood count results.
Got results you are not sure about?
A GP licensed in Spain can go through your HbA1c and other blood tests with you by video, in English or Spanish.
When a test must be repeated
One high result is not always a diagnosis. The WHO advises that a person with no symptoms needs a second test in the diabetes range to confirm it. This can be another HbA1c or a glucose test.
Your doctor will usually repeat a test when:
- A first result is in the diabetes range and you feel well.
- Two different tests disagree.
- Something on the list above may have upset the result.
- The result came from a home kit or pharmacy screening.
If your result is in the higher-risk range, it is usually checked again at regular times. US guidance suggests at least once a year. Your doctor will set the timing for you.
Symptoms that need a quick check
Do not wait for a routine review if you have very high thirst, pass a lot of urine, lose weight without trying, or feel very tired. See a doctor promptly.
Call 112 if you have these signs together with vomiting, deep, rapid breathing, drowsiness or confusion.
What to do after a result in the higher-risk range
A result in the prediabetes range is a warning, not a verdict. Many people never go on to develop diabetes, and lifestyle steps can lower the risk. Useful next steps are:
- Ask which rules your lab or doctor used.
- Check your blood pressure, cholesterol and kidney function too.
- Look at weight, waist size, activity, sleep and smoking with your doctor.
- Agree when to repeat the test.
Weight loss can help, but it should never mean starving yourself. If you have had an eating disorder, tell your doctor first. Our guides on BMI and waist size and PCOS and insulin resistance may also help.
If you already have type 2 diabetes, see what weight loss can and cannot do for remission.
How a GP reviews your results online
Dr. Yelamo reviews lab results by video for adults who are in Spain. Visits run on Tuesday, Thursday, Friday and Saturday. In a review, he will:
- Read the whole report, with its units, dates and reference ranges.
- Compare it with past results, including ones from other countries.
- Ask about symptoms, medicines, pregnancy and blood conditions.
- Explain what the numbers mean under Spanish practice.
- Decide which tests to repeat and when.
- Tell you if you need an exam or tests in person.
If weight is part of the picture, the Weight Optimization consultation is a 30-minute visit focused on weight and metabolic health. Where clinically appropriate, following a genuine evaluation. Treatment and prescriptions are issued solely at the doctor's discretion based on evidence-based clinical guidelines. Any prescription is a private electronic prescription under Spanish law.
Bring a clear photo or PDF of the full report, not a cropped screenshot.
Frequently asked questions
What is a normal HbA1c?
Under ADA rules, below 5.7% (39 mmol/mol) is normal. Under the WHO-based criteria often used in Spain, the higher-risk range starts at 6.0% (42 mmol/mol). Your doctor reads it with your other results and history.
What HbA1c means diabetes?
An HbA1c of 6.5% (48 mmol/mol) or more is in the diabetes range for both the ADA and the WHO. In a person with no symptoms, a second test is usually needed to confirm it.
Why does my Spanish report use mmol/mol?
Many European labs use the international unit, mmol/mol, and some show % as well. Both describe the same result. For example, 6.5% equals 48 mmol/mol.
Do I need to fast for an HbA1c test?
No. HbA1c reflects about three months of blood sugar, so one meal hardly changes it. A fasting glucose test, on the other hand, needs at least eight hours without food.
Can anaemia change my HbA1c?
Yes. Anaemia, haemoglobin variants, pregnancy, blood loss, a recent transfusion, and kidney or liver disease can make HbA1c too high or too low. Your doctor may then use glucose tests instead.
How often should HbA1c be repeated if it is in the prediabetes range?
It depends on your risk. US guidance suggests at least once a year. Your doctor may check sooner if other risk factors or symptoms are present.
Can a GP review my HbA1c online?
Yes. Dr. Yelamo reviews lab results by video for adults in Spain. He explains the numbers, decides what to repeat, and tells you if anything needs an exam in person.
Sources
- American Diabetes Association. 2. Diagnosis and classification of diabetes: Standards of Care in Diabetes 2026. Diabetes Care
- World Health Organization. Use of glycated haemoglobin (HbA1c) in the diagnosis of diabetes mellitus (2011)
- Mata-Cases M et al. Consensus on the detection and management of prediabetes, Spanish Diabetes Society. Rev Clin Esp 2015
- Arranz-Martínez E et al. Prevalence of prediabetes in Spain (SIMETAP-PRED), comparing ADA and SED criteria. Clin Investig Arterioscler 2022
- MSD Manual Professional: diagnostic criteria for diabetes and prediabetes
- CDC: A1C test for diabetes and prediabetes
- NIDDK: recommended tests for identifying prediabetes
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Medical Citations & Sources
This content is written and reviewed by a licensed physician with reference to the following official health authorities.
