What Does Your HbA1c Level Actually Mean?

If your blood test includes HbA1c — and most standard panels do — you've probably glanced at the number and wondered what it actually tells you. It's one of the most clinically important markers in the whole panel. Here's everything you need to know, in plain English.

What is HbA1c and what does it measure?

HbA1c stands for glycated haemoglobin. It's a measure of how much glucose has attached itself to the haemoglobin in your red blood cells over the previous two to three months.

Here's the key idea: glucose is "sticky." When there's more of it circulating in your blood, more of it attaches to haemoglobin. Because red blood cells live for roughly 90 days, your HbA1c reading gives a rolling three-month picture of your average blood sugar levels — rather than just a snapshot of what your glucose was doing at the moment the blood was taken.

Understanding the reference ranges

HbA1c is measured as a percentage (%) in the UK and US, or as mmol/mol (the IFCC unit used across much of Europe). Your lab report may show one or both. They measure the same thing — just expressed differently.

Why HbA1c matters more than a fasting glucose

A fasting blood glucose test gives you a point-in-time reading. Stress, a bad night's sleep, or eating slightly outside your fasting window can all move it. HbA1c doesn't care about any of that — it reflects what's actually been happening in your bloodstream over months.

This makes HbA1c especially useful for:

• Detecting prediabetes early — before fasting glucose has moved out of range
• Monitoring blood sugar control in people already diagnosed with diabetes
• Tracking the effect of lifestyle changes — diet, exercise, weight loss — over a 3–6 month period
• Assessing cardiovascular risk, since elevated HbA1c is an independent risk factor for heart disease even below the diabetes threshold

What can affect your HbA1c result?

HbA1c is robust, but it's not perfect. Several conditions can cause it to read falsely high or falsely low — which is why your doctor should interpret it alongside your full clinical picture.

Things that can cause a falsely high HbA1c

• Iron deficiency anaemia (red blood cells live longer, accumulating more glucose)
• Vitamin B12 or folate deficiency
• Kidney disease (uraemia can affect the test)
• Splenectomy (removal of the spleen)

Things that can cause a falsely low HbA1c

• Haemolytic anaemia (red blood cells are destroyed faster, so less time to accumulate glucose)
• Haemoglobin variants (e.g., sickle cell trait) — certain lab methods may be unreliable
• Recent blood transfusion
• Pregnancy (blood volume changes affect the reading)

How to lower your HbA1c

If your HbA1c has come back in the prediabetes range — or higher than it was last time — the good news is that it is genuinely modifiable. Unlike some markers, you can move HbA1c meaningfully with sustained lifestyle change. The ADA estimates that intensive lifestyle intervention can reduce progression from prediabetes to type 2 diabetes by around 58%.

Dietary changes with the strongest evidence

• Reduce refined carbohydrates and added sugars — white bread, pastries, sugary drinks, and ultra-processed foods spike blood glucose repeatedly. Replacing them with wholegrains, legumes, and vegetables can lower HbA1c by 0.5–1.0% over 3 months.
• Prioritise protein and healthy fats at each meal — these slow glucose absorption and reduce post-meal spikes.
• Eat in a consistent window — time-restricted eating (eating within an 8–10 hour window) has shown promise in reducing HbA1c in several recent RCTs, independent of calorie intake.
• Increase dietary fibre — soluble fibre (oats, legumes, apples) slows glucose absorption. Aim for at least 25–30g per day.

Physical activity

• Resistance training is particularly effective — building muscle increases the body's capacity to take up glucose from the bloodstream. Two to three sessions per week can lower HbA1c by 0.3–0.5%.
• Walking after meals — even a 10–15 minute walk after eating has been shown to blunt post-meal glucose spikes more effectively than a single longer walk at another time of day.
• Aim for 150+ minutes of moderate activity per week — this is the minimum threshold endorsed by both the ADA and NICE for metabolic health.

Sleep and stress

• Chronic sleep deprivation (less than 6 hours) elevates cortisol, which in turn raises blood glucose. Prioritising sleep quality is a legitimate metabolic intervention.
• Psychological stress raises cortisol and can meaningfully worsen HbA1c — particularly in people who are already metabolically vulnerable.

How often should you test?

For people without diabetes or risk factors, testing HbA1c once a year as part of a routine health screen is appropriate. But if your reading has come back elevated, here's a more useful cadence: