HbA1c test results explained: normal, prediabetes and diabetes ranges

HbA1c is one of the most useful numbers on a blood report, and one of the most confusing, because it comes in two different units and the cut-offs differ a little between countries. This guide has HbA1c test results explained step by step: what the number measures, how to read it in % and mmol/mol, and what can throw it off. It's general information, not a diagnosis.

What HbA1c actually measures

Sugar in your blood sticks to haemoglobin, the protein that carries oxygen inside red blood cells. The more sugar there has been in your blood, the more haemoglobin gets coated. Red blood cells live for about two to three months, so HbA1c gives a picture of your average blood sugar over roughly the last three months.

You may also see it called A1C, haemoglobin A1c, glycated haemoglobin or glycohaemoglobin. It's the same test.

A few things follow from this:

• You don't need to fast. A single meal hardly moves it, so the blood can be taken at any time of day.
• It doesn't show highs and lows. Short spikes and dips during the day are smoothed out.
• Recent weeks count most. Your blood sugar over the past month or so has more effect on the result than earlier weeks.

Two units: % and mmol/mol

Labs report HbA1c in one or both of two units:

• Percent (%) is the older unit and is still the one used in the US.
• mmol/mol is the international unit. The UK switched to it in 2009, and many labs now print both.

The two scales are not interchangeable, which is why a result of "53" and a result of "7" can describe the same blood.

HbA1c mmol/mol to %: how to convert

To go from % to mmol/mol: take away 2.15, then multiply by 10.929.

To go from mmol/mol to %: divide by 10.929, then add 2.15.

Here are common values worked out, with the estimated average glucose (eAG) that each one roughly matches. eAG is a long-term average, so it won't match any single meter reading.

HbA1c %	HbA1c mmol/mol	eAG mmol/L	eAG mg/dL
6.0	42	7.0	126
6.5	48	7.8	140
7.0	53	8.6	154
7.5	58	9.4	169
8.0	64	10.2	183
9.0	75	11.8	212
10.0	86	13.4	240

The mmol/mol and mmol/L columns come from an NHS conversion table, and the mg/dL column from the American Diabetes Association.

HbA1c test results explained: normal, prediabetes and diabetes

These are the ranges used to check adults for type 2 diabetes. Notice that US and UK guidance draw the prediabetes line in slightly different places.

HbA1c %	HbA1c mmol/mol	What it usually means
Below 5.7	Below 39	Normal range
5.7 to 5.9	39 to 41	Prediabetes in US guidance; normal in UK guidance
6.0 to 6.4	42 to 47	Prediabetes in both US and UK guidance
6.5 or above	48 or above	In the diabetes range; usually confirmed with a second test

US figures are from the NIDDK and CDC. UK figures are from Diabetes UK and NHS Scotland.

What a "normal HbA1c" means

A normal HbA1c is a good sign, but it's a snapshot. If you have risk factors for type 2 diabetes, your doctor will tell you when to recheck.

What the prediabetes HbA1c range means

The prediabetes HbA1c range means your blood sugar has been higher than ideal, but not high enough to count as diabetes. Within that range, the higher the number, the higher the risk. US guidance suggests rechecking every one to two years.

In the diabetes range

One result of 6.5% (48 mmol/mol) or above is not enough on its own if you have no symptoms. Guidance in both the US and UK is to repeat the test, or confirm it with a glucose test, before a diagnosis is made. HbA1c is also not the right test for diagnosing type 1 diabetes or diabetes that starts in pregnancy.

Lab test or clinic test?

For diagnosis, US guidance says the blood should come from a vein and go to a lab that uses a certified method. Quick "point-of-care" HbA1c tests done in a clinic can be useful, but they shouldn't be used on their own to diagnose diabetes.

HbA1c versus a finger-prick glucose test

These two numbers answer different questions. A finger-prick glucose reading is a snapshot of your blood sugar at that moment, and it changes with food, activity and stress. HbA1c is a slow-moving average of the past two to three months. People taking insulin or some other diabetes medicines often need both: finger-pricks to manage each day, and HbA1c to see the bigger picture.

If you already have diabetes

HbA1c is the main way your diabetes team checks how things are going over time.

• Targets are personal. The American Diabetes Association suggests 7% (53 mmol/mol) or less for most adults with diabetes. Diabetes UK describes 48 mmol/mol (6.5%) or below as ideal. Your own target may be higher if low blood sugar is a risk for you.
• How often: often every three to six months, and at least once or twice a year.
• Small changes are normal. Repeat tests vary a little even on the same sample. The NIDDK gives the example that a 6.8% result could come back anywhere from 6.4% to 7.2% on a repeat.

What affects HbA1c

Because HbA1c depends on red blood cells and haemoglobin, anything that changes them can make the number misleading. Ask your doctor about this if any of these apply to you:

• Anaemia. Very low iron can make HbA1c falsely high. Other blood disorders can affect it too.
• Recent blood loss or a transfusion. These change the mix of red blood cells, so HbA1c may not be reliable for a while afterwards.
• Some haemoglobin variants. Inherited differences in haemoglobin, more common in people with African, Mediterranean or Southeast Asian heritage, and conditions such as sickle cell disease or thalassaemia, can interfere with some lab methods. Most people with a variant have no symptoms and may not know. Not every lab method is affected.
• Pregnancy. Early in pregnancy, the result can still reflect blood sugar from before pregnancy. US guidance lists both early and late pregnancy as times when results can be off.
• Kidney failure, liver disease and dialysis. These can change results.
• Some medicines. US guidance names opioids and some HIV medicines, and Diabetes UK mentions steroids. Never stop a medicine without talking to your doctor.
• Being unwell or under a lot of stress. Diabetes UK lists both as things that can change your result.

A useful clue: if your HbA1c and your glucose readings don't seem to match, tell your doctor. They may suggest a different test.

Questions to ask about your result

• Which unit is my result in, and which cut-offs does my lab use?
• Is this result new, or part of a trend?
• Could anaemia, a recent illness, blood loss or a medicine be affecting it?
• What target makes sense for me, and when should I retest?

When to get urgent help

HbA1c itself is never an emergency, but very high blood sugar can be. Call your local emergency number or go to an emergency department if you have high blood sugar and you feel or are sick, have stomach pain, are breathing faster than usual, feel very drowsy or confused, notice a fruity smell on your breath, or have high ketones.

Watching the trend

HbA1c is most helpful across several tests. If you upload your reports to Saluvo, two AI models read each one, you confirm any value they disagree on, and you can see how your HbA1c moves from report to report. Bring that trend to your next appointment so you and your doctor can decide what it means.