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A1C 5.7 to 6.4: What a Prediabetes Result Means and What to Do Next

An A1C of 5.7% to 6.4% (39 to 47 mmol/mol) means prediabetes in the US. The UK uses 42 to 47. Dr. Sayantan Banerjee explains the numbers and the first steps that work.

PREDIABETES REMISSION

Dr. Sayantan Banerjee

10/31/20268 min read

You had a routine blood test, and the report says your A1C is 5.8%, or your HbA1c is 43 mmol/mol. Your doctor might have said "borderline" or "keep an eye on it". Maybe nobody said anything at all, and you found the number yourself in your patient portal or NHS app.

That number deserves more attention than it usually gets. It is also one of the most fixable results you can be given. This article explains what A1C measures, how the US and UK interpret it differently, what a prediabetes result means for your future, and what to do in the next few weeks.

What A1C actually measures

Glucose in your blood sticks to haemoglobin, the protein inside red blood cells that carries oxygen. The higher your average glucose, the more of your haemoglobin becomes coated, or glycated. HbA1c, often written A1C in the US, is the percentage of haemoglobin that is glycated.

Red blood cells live for about three months, so A1C reflects your average glucose over roughly the previous two to three months. That makes it more stable than a single glucose reading, which can change a lot from hour to hour. It also means you don't need to fast before the test.

The US usually reports A1C as a percentage. The UK and many other countries use mmol/mol. Both describe the same thing.

5.4 — HbA1c (mmol/mol): 36; Approximate average glucose: 108 mg/dL (6.0 mmol/L)
5.7 — HbA1c (mmol/mol): 39; Approximate average glucose: 117 mg/dL (6.5 mmol/L)
6.0 — HbA1c (mmol/mol): 42; Approximate average glucose: 126 mg/dL (7.0 mmol/L)
6.2 — HbA1c (mmol/mol): 44; Approximate average glucose: 131 mg/dL (7.3 mmol/L)
6.4 — HbA1c (mmol/mol): 46; Approximate average glucose: 137 mg/dL (7.6 mmol/L)
6.5 — HbA1c (mmol/mol): 48; Approximate average glucose: 140 mg/dL (7.8 mmol/L)

The average glucose column is an estimate based on a standard formula. Individual results vary.

The numbers, in US and UK units

The US and UK use slightly different cut-offs and different words. In the US it is called prediabetes. NHS letters often say non-diabetic hyperglycaemia, or "at risk of type 2 diabetes".

HbA1c / A1C — Normal: below 5.7% (39 mmol/mol); Prediabetes (ADA, US): 5.7 to 6.4% (39 to 47 mmol/mol); UK at-risk range (NICE/NHS): 6.0 to 6.4% (42 to 47 mmol/mol); Diabetes: 6.5% (48 mmol/mol) or above
Fasting glucose — Normal: below 100 mg/dL (5.6 mmol/L); Prediabetes (ADA, US): 100 to 125 mg/dL (5.6 to 6.9 mmol/L); UK at-risk range (NICE/NHS): 5.5 to 6.9 mmol/L; Diabetes: 126 mg/dL (7.0 mmol/L) or above
2-hour glucose test — Normal: below 140 mg/dL (7.8 mmol/L); Prediabetes (ADA, US): 140 to 199 mg/dL (7.8 to 11.0 mmol/L); UK at-risk range (NICE/NHS): 7.8 to 11.0 mmol/L; Diabetes: 200 mg/dL (11.1 mmol/L) or above

So someone with an A1C of 5.8% would be told they have prediabetes in the US, but might be told their result is normal in the UK. The biology is the same in both cases. Risk rises steadily as A1C climbs, and there is no sharp line at which it switches on. The cut-offs are agreed conventions, not biological boundaries.

How common is it?

Very. The CDC's latest estimate is 115.2 million American adults with prediabetes. The CDC also says about 8 in 10 people with prediabetes don't know they have it.

In the UK, Diabetes UK estimates 6.9 million people are at increased risk of type 2 diabetes based on their blood sugar levels, and that almost 1.3 million people are living with type 2 diabetes but haven't yet been diagnosed.

Who is most at risk?

Prediabetes is more likely if you:

are 45 or older, although it is increasingly common in younger adults
have overweight or obesity, especially around the waist
have a parent, brother or sister with type 2 diabetes
are physically active less than three times a week
had diabetes during pregnancy (gestational diabetes) or gave birth to a baby weighing more than 9 lb (about 4 kg)
have polycystic ovary syndrome (PCOS)
are of South Asian, Black African, African-Caribbean, Hispanic or Latino, American Indian, Alaska Native or Pacific Islander heritage
have high blood pressure, high triglycerides or low HDL cholesterol
have fatty liver disease
sleep poorly or have sleep apnoea

If several of these apply, regular testing is sensible even if you feel well.

What does it mean for your future?

Prediabetes isn't a disease you usually feel. Most people have no symptoms at all. What it tells you is that your body is working harder than it should to keep glucose in range, usually because the liver and muscles have become resistant to insulin.

A review published in The Lancet in 2012 estimated that about 5% to 10% of people with prediabetes develop type 2 diabetes each year, and that up to 70% eventually do over a lifetime. A higher A1C, a bigger waist and a family history all push the risk up.

It isn't only about diabetes. Prediabetes is also linked to a higher risk of heart disease, stroke, fatty liver and kidney problems. A large 2020 review in The BMJ found that prediabetes was associated with a modestly higher risk of heart disease and death, even before diabetes develops.

But the outcome isn't fixed. In the US Diabetes Prevention Program, a lifestyle programme cut the risk of developing type 2 diabetes by 58%. People who got their glucose back to normal even once had a much lower risk of diabetes in the years that followed. I cover that research in detail in my article on reversing prediabetes.

Can one test be wrong?

One A1C result can be thrown off by several things. Iron deficiency can push A1C up. Some anaemias, recent blood loss or transfusion, chronic kidney disease, pregnancy, and inherited haemoglobin variants can push it up or down. These variants are more common in people of African, Mediterranean, Middle Eastern and South Asian heritage.

If your A1C and fasting glucose don't agree, or if your result is very close to a cut-off, your doctor may suggest repeating the test or using a different one. A 2-hour oral glucose tolerance test is the most sensitive, but it is less convenient, because you need to fast, drink a glucose solution and wait two hours.

But if two tests point the same way, take it seriously. That doesn't mean panic. It means acting while the numbers are still easy to move.

What to do in the next month

Ask for your exact numbers. Get the A1C in both % and mmol/mol, and your fasting glucose if it was measured. Write them down with the date.
Get the full picture. Ask for blood pressure, cholesterol including triglycerides and HDL, kidney function and liver tests. Measure your waist. A waist more than half your height is a warning sign on its own.
Ask about a prevention programme. In the US, look for a CDC-recognised National Diabetes Prevention Program. Many run online, and Medicare covers one version for eligible people. In England, ask your GP about the NHS Diabetes Prevention Programme, called Healthier You.
Pick one change you can keep. A 10 to 15 minute walk after your largest meal, swapping sugary drinks for water, or adding a portion of beans or lentils to dinner are good places to start.
Look at sleep. If you regularly sleep less than seven hours, or snore heavily, address it. Poor sleep worsens insulin resistance.
Book a retest. ADA and NHS guidance both suggest checking at least once a year. Many people like to retest after three to six months to see their progress.

What to expect when you start making changes

Glucose can respond quickly. Some people see their fasting glucose fall within a few weeks of eating fewer refined carbohydrates, being more active and losing a little weight. A1C takes longer to move, because it reflects three months of glucose. A drop of 0.2% to 0.5% (2 to 5 mmol/mol) over three to six months is a realistic and meaningful change for many people.

The biggest lever is usually weight. In the Diabetes Prevention Program, the goal was to lose 7% of body weight, which is about 6 kg (14 lb) for someone weighing 90 kg (198 lb). Physical activity was the second lever, at 150 minutes a week of brisk walking or similar.

If your weight is already in the healthy range, focus on activity, food quality, sleep and waist size. Some people, especially of South Asian heritage, develop prediabetes at a normal BMI because they carry more fat around the organs.

Talking to your doctor

Some doctors don't mention prediabetes, especially when the result is just above the cut-off. That doesn't mean it doesn't matter. Useful questions include:

Is my result in the prediabetes or at-risk range?
Should we repeat it, or check with a different test?
What other tests should I have?
Do I qualify for a prevention programme?
When should I be retested?
Would metformin or any other medicine be appropriate for me?

Special situations

After gestational diabetes. Women who had diabetes during pregnancy have a much higher lifetime risk of type 2 diabetes. In the US, the ADA recommends testing four to twelve weeks after the birth, then at least every three years for life. In the UK, NICE recommends a test after the birth and then an annual HbA1c. If you had gestational diabetes and haven't been tested recently, ask your GP or doctor.

During pregnancy. A1C is less reliable in pregnancy, because red blood cell turnover changes. Doctors usually use glucose tolerance tests instead. If you have prediabetes and are planning a pregnancy, talk to your doctor beforehand, since good glucose control before conception matters.

Older adults. Prediabetes is very common over 65. In the Diabetes Prevention Program, people aged 60 and over had the largest benefit from lifestyle change, a 71% reduction in risk. For older adults, the focus is often on activity, strength, balance and good nutrition, with careful weight loss if needed, so that muscle is protected.

Younger adults and teenagers. Prediabetes is increasingly found in people in their 20s and 30s, and in teenagers with obesity. Type 2 diabetes that starts young tends to progress faster, so acting early matters even more.

People with a normal BMI. If your weight is in the healthy range but your A1C is raised, look at your waist, activity levels, sleep, family history and diet quality. People of South Asian heritage often develop prediabetes at lower weights and benefit from the same changes.

In all of these situations, the same core steps apply: know your numbers, move more, improve your diet, sleep well, and retest.

How my book can help

The Prediabetes Exit Strategy was written for people at exactly this point. It explains insulin resistance in plain terms and sets out practical changes to eating, movement, sleep and daily routine, along with simple metabolic strategies. You can read more on the book page.

Frequently asked questions

Is an A1C of 5.7 bad? It is the lowest end of prediabetes in the US. It is a signal to act, not a diagnosis of diabetes.

Can prediabetes go away? Yes. Many people return to normal glucose with weight loss and more activity.

What is 6.0% A1C in mmol/mol? About 42 mmol/mol, which is the start of the UK at-risk range.

Do I need to fast for an A1C test? No. A1C reflects the past few months, so fasting isn't needed.

How often should I be tested? At least once a year if you have prediabetes, and more often if you are making changes and want to track progress.

Can I have prediabetes and be slim? Yes. It is less common but does happen, especially with a family history, inactivity, or more fat around the waist and organs.

Will I definitely get diabetes? No. Many people with prediabetes never develop diabetes, especially if they make changes.