Educational summary — not medical advice. Discuss with your healthcare provider.
Informed by recognized medical guidance
Overview
The HbA1c test is a blood test that measures your average blood sugar (glucose) levels over the past 2 to 3 months. Unlike a finger-prick check that gives you a snapshot of your sugar right now, this test shows how well your sugar has been controlled over time. Doctors mainly use it to diagnose and monitor type 2 diabetes.
Key facts
HbA1c stands for glycated haemoglobin — sugar attached to the part of your red blood cells that carries oxygen.
The test does not require fasting — you can eat and drink normally beforehand.
A higher HbA1c number means higher average blood sugar levels over the previous months.
Yes. The HbA1c test is very common and is used worldwide for diabetes management and diagnosis.
It affects anyone who has or is at risk of type 2 diabetes. This includes people over 40, those who are overweight, and people with a family history of diabetes. It is also used for pregnant women to check for gestational diabetes.
Questions about this article
Symptoms
Call emergency services immediately if you notice:
Very high blood sugar (over 20 mmol/L) with confusion or severe dehydration
Breathing very fast or deep (Kussmaul breathing)
A fruity smell on the breath (ketones)
Unconsciousness or seizures
See a doctor urgently (same day) if you notice:
⚠Blood sugar consistently above 15 mmol/L for several days
⚠Signs of infection (fever, chills) in a person with diabetes
⚠Nausea, vomiting, or abdominal pain that makes it hard to keep fluids down
Common symptoms
Feeling very thirsty often
Urinating more frequently, especially at night
Feeling more tired than usual
Blurred vision
Symptoms in children
Unexplained weight loss despite normal eating
Frequent infections, such as thrush or skin boils
Irritability or mood changes
Symptoms in older adults
Increased thirst and urination
Unexplained weight loss
Blurred vision
Slower healing of cuts or bruises
Causes
Main causes
A high HbA1c result is usually caused by persistently high blood sugar levels, which is the hallmark of diabetes.
Temporary high readings can also happen with illness, stress, or certain medications.
Risk factors
Being overweight or obese
Having a family history of type 2 diabetes
Being over 40 years of age
Having high blood pressure or high cholesterol
Being of South Asian, African-Caribbean, or Black African descent (higher risk at a younger age)
Previous diagnosis of gestational diabetes
When to see a doctor
See a doctor urgently if:
If you have any of the emergency symptoms listed above, call your local emergency number immediately.
If your blood sugar is very high (e.g., over 20 mmol/L) and you feel unwell.
Book a routine appointment if:
If you have symptoms that suggest high blood sugar (thirst, frequent urination, weight loss), see your doctor for a blood test.
If you are over 40 and have risk factors, ask your doctor about a routine HbA1c test.
If you have diagnosed diabetes, you will have regular HbA1c tests every 3 to 6 months as part of your management plan.
The HbA1c test is quick and simple. It does not require fasting, and the result gives you a clear picture of your blood sugar control. If your result is high, your healthcare team will help you understand what it means and what to do next.
Diagnosis
The HbA1c test is used to diagnose type 2 diabetes and prediabetes. A single high result is usually confirmed with a repeat test on a different day. For diagnosis, the levels are: normal below 42 mmol/mol, prediabetes 42–47 mmol/mol, diabetes 48 mmol/mol or above.
Tests that may be done
HbA1c blood test (taken from a vein in your arm)
Fasting blood glucose test (sometimes used instead, but less common for initial diagnosis)
Oral glucose tolerance test (OGTT) – used especially in pregnancy
What to expect at your appointment
A healthcare professional will take a small sample of blood from your arm. You do not need to fast. The sample is sent to a lab, and you usually get your result within a few days. The test is safe and the only risk is slight bruising at the puncture site.
Treatment
Treatment for high HbA1c focuses on lowering your average blood sugar to a healthy range. This is usually done through lifestyle changes and medication. The goal is to prevent complications and improve quality of life. Treatment is tailored to each person and may be adjusted over time.
Self-care at home
Monitor your blood sugar at home as advised by your healthcare team.
Take your diabetes medication or insulin exactly as prescribed.
Track your food intake and physical activity to see how they affect your blood sugar.
Attend all follow-up appointments and tests.
Medical treatments
Medications for type 2 diabetes work in different ways – some help your body make more insulin, some help it use insulin better, and some slow down how fast sugar enters your blood. Your doctor will choose a treatment that suits your health, weight, and lifestyle. Some people may also need insulin injections. Always follow your doctor's advice and never change your medication without consulting them.
When is surgery considered?
Surgery is not a direct treatment for high HbA1c. However, in some cases of severe obesity and type 2 diabetes, weight-loss (bariatric) surgery may be considered after a thorough assessment. This is only for specific people and is not common.
Living with this condition
If your HbA1c is high, you will need to manage your blood sugar every day. This means eating regular meals, being active, taking medication as prescribed, and checking your blood sugar when recommended. Over time, these habits become part of your routine and help you feel better.
Lifestyle tips
Eat a balanced diet with plenty of vegetables, whole grains, and lean proteins.
Limit sugary drinks, sweets, and processed foods.
Aim for at least 150 minutes of moderate activity each week (e.g., brisk walking, cycling).
Get enough sleep – poor sleep can raise blood sugar.
Avoid smoking and limit alcohol.
Diet and exercise
Eating smaller, regular meals and choosing low glycaemic index foods (like oats, lentils, and non-starchy vegetables) can help keep blood sugar steady. Exercise helps your body use insulin more effectively. Even a short walk after meals can lower your blood sugar. Always check with your doctor before starting a new exercise routine.
Mental health and emotional wellbeing
Living with a high HbA1c or diabetes can be stressful. It is common to feel worried, frustrated, or overwhelmed. Talking to a friend, family member, or a mental health professional can help. Some people find support groups or online communities helpful. If you are struggling with your mood, speak to your healthcare team – they can help.
Prevention
You cannot always prevent high HbA1c, especially if you have a strong genetic risk. However, many cases of type 2 diabetes can be prevented or delayed. The best ways are to maintain a healthy weight, eat a balanced diet, and stay active. If you have prediabetes (HbA1c 42–47 mmol/mol), these steps are especially effective.
Vaccines
People with diabetes should have their yearly flu vaccine and the pneumococcal vaccine (to prevent pneumonia). Ask your doctor about which vaccinations you need.
Screening programmes
If you are over 40, you can ask your GP to check your HbA1c every 1–3 years, especially if you have risk factors. The NHS offers a free health check for adults aged 40–74 that includes this test.
Complications
If left untreated
Damage to small blood vessels in the eyes (retinopathy) – can lead to vision loss
Kidney damage (nephropathy) – can progress to kidney failure
Nerve damage (neuropathy) – causes numbness, tingling, or pain in hands and feet
Increased risk of heart attack and stroke
Slow healing of wounds, which can lead to infections and amputations
Long-term outlook
With good blood sugar control, many people with high HbA1c live full, healthy lives. Lowering your HbA1c by even a small amount (like 5–10 mmol/mol) can significantly reduce your risk of complications. Your healthcare team will work with you to find the best approach. It is never too late to make positive changes.
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Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: July 8, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.
