Prediabetes Blood Tests: HbA1c, Glucose and Insulin

Prediabetes means your blood sugar is higher than it should be, but not high enough to be type 2 diabetes. NHS services also call it non-diabetic hyperglycaemia. Diabetes UK notes that there are not usually any symptoms, so most people find out from a routine blood test.

Prediabetes matters because it raises your risk of type 2 diabetes, but it is also a chance to act early. This guide explains which blood tests diagnose prediabetes, when HbA1c can be misleading, where fasting insulin fits, the free NHS programme you may be offered and how often to retest. For a full explanation of the numbers, see our guides to HbA1c levels and insulin levels.

Test it in Chiswick: our HbA1c blood test costs £59, with your result explained in person by a practitioner. No GP referral needed. Book this test or call 020 4515 0000.

Quick answer

HbA1c is the main blood test for prediabetes: 42 to 47 mmol/mol means a higher risk of type 2 diabetes, and 48 mmol/mol or above is in the diabetes range, which needs a repeat test to confirm if you have no symptoms. Under NICE guidance, a fasting glucose of 5.5 to 6.9 mmol/l also counts as high risk. HbA1c can mislead in pregnancy, some types of anaemia and some inherited blood conditions. If you are in the prediabetes range, retest at least once a year and ask your GP about the NHS Diabetes Prevention Programme.

Blood tests that can help

HbA1c

HbA1c shows your average blood sugar over the past 2 to 3 months, and you do not need to fast for it. As a guide from NHS laboratory and Diabetes UK guidance:

• Below 42 mmol/mol: not in the prediabetes or diabetes range.
• 42 to 47 mmol/mol: prediabetes (non-diabetic hyperglycaemia), a higher risk of type 2 diabetes.
• 48 mmol/mol or above: in the diabetes range. If you have no symptoms, NHS guidance is to repeat the test, ideally in the same laboratory, to confirm it.

Our HbA1c test costs £59. The Cholesterol and HbA1c Check (£59) adds a full blood count, cholesterol and CRP, and the full blood count can flag anaemia that may affect HbA1c.

Fasting glucose

A fasting plasma glucose measures your blood sugar after an overnight fast. NICE guidance uses 5.5 to 6.9 mmol/l to identify people at high risk, and 7.0 mmol/l or above is in the diabetes range. Some NHS laboratories use the World Health Organization cut-off of 6.1 mmol/l for impaired fasting glucose instead, so the wording on your report may differ. Our Glucose test costs £39. See do I need to fast before a blood test.

When HbA1c is not reliable

HbA1c depends on how long your red blood cells survive, so some conditions make it read falsely high or low. NHS laboratory guidance lists:

• pregnancy, where gestational diabetes is diagnosed with glucose tests
• inherited haemoglobin variants such as sickle cell trait or thalassaemia, haemolytic anaemia, severe or recent blood loss and removal of the spleen
• iron and B12 deficiency, which have a smaller effect
• advanced kidney disease and dialysis, and HIV treatment
• symptoms that came on quickly, suspected type 1 diabetes, children, and medicines that raise sugar quickly such as steroids

In these situations, glucose tests are used instead, and your practitioner will advise.

Fasting insulin and HOMA-IR: optional extras

Fasting insulin is not part of how the NHS diagnoses prediabetes. NHS hospital laboratories mainly measure insulin to investigate low blood sugar, and HOMA-IR, a score calculated from fasting insulin and glucose, was developed for research. There is no agreed UK cut-off, and results vary between laboratory methods. That said, alongside HbA1c, weight, waist size and cholesterol, a fasting insulin result can help build a fuller picture of insulin resistance and track change over time. Our Insulin test costs £79. Read insulin levels explained.

Cholesterol

NHS guidance says people with prediabetes should have an annual check that includes HbA1c and a heart and circulation (vascular) risk assessment. A Cholesterol Profile (£49) covers total, LDL and HDL cholesterol and triglycerides. See our guide to cholesterol levels.

If your result is in the prediabetes range

Healthier You, the NHS Diabetes Prevention Programme, is a free 9-month programme to help you make changes to diet, activity and weight, offered face to face in groups, digitally or remotely. NHS services list these eligibility criteria: aged 18 or over, an HbA1c of 42 to 47.9 mmol/mol or a fasting glucose of 5.5 to 6.9 mmol/l in the last 12 months, registered with a GP, and not pregnant. Your GP can refer you, and in many areas you can self-refer using your result, the test date and your NHS number. Ask for a GP feedback report so your GP has a record of your result.

Diabetes UK says it is possible to bring your blood sugar back below 42 mmol/mol. Retest at least once a year, or sooner if your practitioner advises. Our guide to what causes type 2 diabetes explains the risk factors.

Which test should I book?

• A focused start: Diabetes Status, £69. HbA1c, glucose, insulin and C-peptide. Fast overnight so the glucose and insulin results can be read properly.
• A broader picture: Insulin Resistance Check (HOMA-IR), £99. Fasting glucose, insulin and a calculated HOMA-IR score. It does not include HbA1c, so pair it with an HbA1c test.
• The fullest view: Metabolic Health Extended, £99. HbA1c, glucose, insulin and C-peptide plus a detailed cholesterol profile (including apolipoprotein B, lipoprotein(a) and small LDL), CRP, high sensitivity CRP and adiponectin.

What blood tests cannot tell you

A blood test shows where your blood sugar is now, not whether you will go on to develop diabetes. One result in the diabetes range does not confirm diabetes without symptoms; it needs a repeat test. An HbA1c below 48 mmol/mol does not rule out diabetes diagnosed with glucose tests. Telling type 1 from type 2 diabetes needs other tests and a medical assessment, and the oral glucose tolerance test, used in pregnancy and some other situations, is arranged through your GP or hospital and is not offered at our clinic.

When to see a GP urgently

See a GP soon if you have possible symptoms of type 2 diabetes:

• feeling very thirsty or tired
• peeing more than usual
• losing weight without trying
• blurred vision, cuts that are slow to heal, or repeated thrush

Call 999 or go to A&E if you have symptoms of diabetic ketoacidosis, such as being sick, stomach pain, breathing more deeply than usual, breath that smells fruity, or feeling sleepy or confused. The NHS says this applies even if you have not been diagnosed with diabetes.

Frequently asked questions

Is an HbA1c of 42 prediabetes?

Yes. An HbA1c of 42 to 47 mmol/mol is in the prediabetes range, meaning a higher risk of type 2 diabetes. It is a prompt for lifestyle changes and yearly retesting, not a diabetes diagnosis.

Can prediabetes go back to normal?

It can. Diabetes UK says it is possible to bring your blood sugar back to a normal level, below 42 mmol/mol, and the NHS Diabetes Prevention Programme is designed to help.

Do I need to fast for a prediabetes blood test?

Not for HbA1c. You do need to fast overnight for a fasting glucose or fasting insulin test, so check which tests are in your panel when you book.

How often should I be retested?

At least once a year if you are in the prediabetes range. NHS guidance also suggests yearly checks for people with a normal result who are at high risk, for example after gestational diabetes.

Should I have a fasting insulin test?

It is optional. It is not needed to diagnose prediabetes, but some people find it useful to track insulin resistance over time alongside HbA1c and weight.

Prediabetes blood tests in Chiswick

Omnia Lifestyle is at 8 to 9 Bedford Corner, The Avenue, Chiswick, London W4 1LZ, a short walk from Turnham Green station (District line; Piccadilly line trains stop there early morning and late evening only) and served by buses 94, E3 and 272. Limited parking is available on request when you book. Every clinic test price includes your sample taken at the clinic, analysis at the Randox accredited laboratory, a practitioner review of your result with you, and a GP feedback report on request. You do not need a GP referral, and most results are back within a few working days.

Useful links: book an HbA1c test or the Metabolic Health Extended panel, add a Cholesterol Profile, or compare every blood test and price. Our guides to HbA1c levels and insulin levels explain the numbers. If you would like support alongside your GP care, see our type 2 diabetes and metabolic health care at Omnia.

This article is general information, not medical advice. Discuss your results with your GP or practitioner.