HbA1c - glycated haemoglobin - is one of the most important numbers in diabetes care, yet many patients leave their GP surgery unsure what it actually means. Unlike a fingerprick glucose test that shows your blood sugar at a single moment in time, HbA1c reflects your average blood glucose over the past 2-3 months by measuring how much sugar has attached to red blood cells.
The science is elegant. Red blood cells live for approximately 90-120 days, and as they circulate, glucose molecules gradually bind to haemoglobin in a process called glycation. The higher your blood sugar over that period, the more HbA1c accumulates. This makes it an excellent long-term indicator - you cannot game it with a healthy breakfast the morning of your blood test.
“The science is elegant. Red blood cells live for approximately 90-120 days, and as they circulate, glucose molecules gradually bind to haemoglobin in a process called glycation. The higher your blood sugar over that period, the more HbA1c accumulates. This makes it an excellent long-term indicator - you cannot game it with a healthy breakfast the morning of your blood test.”
Results are reported in mmol/mol in the UK and Europe, or as a percentage in the USA. Normal is below 42 mmol/mol (6.0%). Prediabetes falls between 42-47 mmol/mol (6.0-6.4%), and a diagnosis of Type 2 diabetes is typically made at 48 mmol/mol (6.5%) or above, confirmed by a second test. Our HbA1c Calculator converts between units and estimates your average blood glucose from the result.
HbA1c is a powerful predictor of long-term complications. Data from the landmark UKPDS trial showed that each 1% reduction in HbA1c was associated with a 37% reduction in microvascular complications and a 14% reduction in heart attack risk. These are not marginal improvements - they represent a dramatically different health trajectory.
Diet, exercise, and medication all move HbA1c meaningfully. A low-glycaemic diet rich in fibre, vegetables, and lean protein consistently reduces levels. Aerobic exercise improves insulin sensitivity, and high-intensity interval training has been shown in multiple trials to reduce HbA1c by 0.5-1.0% in people with Type 2 diabetes. Even a modest 5-7% reduction in body weight can reverse prediabetes entirely - bringing HbA1c back into the normal range.
HbA1c does have limitations worth knowing. Anaemia, haemoglobin variants (common in people of African, Mediterranean, or South Asian heritage), and certain medications can produce falsely high or low results. It also does not capture blood sugar variability - someone with frequent extreme highs and lows might have an average HbA1c yet still be at risk. Continuous glucose monitoring (CGM) is increasingly used alongside HbA1c for a fuller picture.
If your result falls in the prediabetes range, act now. The condition is almost entirely reversible at that stage through lifestyle changes alone, and catching it early is one of the most powerful preventive health actions you can take. Check your numbers with our Blood Sugar Checker and HbA1c Calculator.