The UK bands
| Result (mmol/mol) | Percentage | What it means |
|---|---|---|
| Below 42 | Below 6.0% | Normal |
| 42 to 47 | 6.0% to 6.4% | Non-diabetic hyperglycaemia (prediabetes) |
| 48 and above | 6.5% and above | Diabetes range |
These are the WHO thresholds used by NICE and the NHS. A diagnosis of diabetes needs two results at or above 48, or one result plus symptoms; a single number never diagnoses on its own.
For people already diagnosed, NICE sets treatment targets rather than diagnostic thresholds: usually 48 mmol/mol (6.5%) for those managing with diet or a drug that does not cause hypos, and 53 mmol/mol (7.0%) where the treatment carries a hypo risk.
Conversion table
| mmol/mol | % | Average glucose (mmol/L) |
|---|---|---|
| 31 | 5.0 | 5.4 |
| 39 | 5.7 | 6.5 |
| 42 | 6.0 | 7.0 |
| 47 | 6.4 | 7.7 |
| 48 | 6.5 | 7.8 |
| 53 | 7.0 | 8.6 |
| 58 | 7.5 | 9.3 |
| 64 | 8.0 | 10.2 |
| 75 | 9.0 | 11.8 |
| 86 | 10.0 | 13.4 |
The formula, if you want it: percentage = (mmol/mol ÷ 10.929) + 2.15. Average glucose in mmol/L = (1.5944 × percentage) − 2.5944. The average-glucose figure is an estimate from a population study, not a measured value.
What a result of 42 actually means
Forty-two is the number people search for most, because it is the exact line between normal and raised. A result of 41 is normal; 42 is the bottom of the prediabetes band. Nothing biological changes across that gap, which is worth holding onto: the thresholds are administrative lines drawn across a smooth gradient of risk.
What matters more is where you were last time. A result of 42 that was 42 four years ago is stable. A result of 41 that was 34 four years ago is moving quickly in the wrong direction while still sitting inside the normal band, and no single reading would ever tell you that.
Being in the 42 to 47 range usually qualifies you for the NHS Healthier You programme, which cut progression to type 2 diabetes substantially in trials of this approach.
What HbA1c misses
HbA1c is an average, and averages hide things. Two people can share a result of 44 while one has steady glucose all day and the other swings high after every meal.
It is also unreliable in several situations, worth knowing before you act on a number:
- Anaemia and iron deficiency can push the result either way
- Sickle cell trait, thalassaemia, and other haemoglobin variants interfere with the measurement
- Recent blood transfusion or significant blood loss makes it meaningless
- Pregnancy: HbA1c is not used to diagnose gestational diabetes
- Advanced kidney disease and some medications distort it
If any of these apply, your GP will use fasting glucose or an oral glucose tolerance test instead.
The bigger gap is timing. HbA1c rises late. Fasting insulin climbs years earlier, while glucose still looks fine, because a pancreas working overtime can hold the average down for a long while. That is the case for looking at more than one marker: the triglyceride to HDL ratio from a standard lipid panel gives you a second early read at no extra cost.
Where HbA1c fits with your other numbers
Raised fasting glucose is one of the five components of metabolic syndrome, and HbA1c is the practical stand-in most UK patients actually have. Blood pressure is another component: check yours with the blood pressure checker. A guide to what family history really means for your diabetes risk is coming next.
Watch the direction, not the single number
One HbA1c tells you your average over three months. Four of them, across four years, tell you which way your metabolism is heading, and that is the information you can still do something about.
BioMetRx stores every HbA1c you enter, converts the units for you, and plots it against your blood pressure, weight, waist, and lipid results. See how it works.
Frequently asked questions
What is HbA1c 42 in percentage?
42 mmol/mol is 6.0 per cent. It is the bottom of the UK prediabetes band, called non-diabetic hyperglycaemia by the NHS.
What is a normal HbA1c in the UK?
Below 42 mmol/mol, which is below 6.0 per cent. Between 42 and 47 is prediabetes; 48 and above is the diabetes range.
How do I convert HbA1c from mmol/mol to percentage?
Divide by 10.929 and add 2.15. So 48 ÷ 10.929 = 4.39, plus 2.15 gives 6.5 per cent. The converter on this page does it both ways.
Why did my HbA1c units change?
UK labs switched from percentages to mmol/mol in 2011 to align with the international IFCC standard. Old results and most books still use the percentage.
Is HbA1c 45 bad?
It sits in the middle of the prediabetes band, which means raised but not diabetic. It is the range where diet and activity changes have the most effect, and it usually qualifies you for the NHS prevention programme.
Can HbA1c be wrong?
Yes. Anaemia, inherited haemoglobin variants such as sickle cell trait, recent transfusion, pregnancy, and advanced kidney disease all distort it. Your GP would use a different test in those situations.
This page uses WHO / NICE HbA1c thresholds and is educational, not a diagnosis. See our medical disclaimer.