What does your HbA1c really mean in everyday terms?

The ADA defines normal as below 5.7% (39 mmol/mol). Prediabetes is 5.7-6.4% (39-46 mmol/mol). Diabetes is diagnosed at 6.5% (48 mmol/mol) or above. For people already diagnosed with diabetes, the ADA target for most adults is below 7.0%.

Key conversions: 5.7% = 39 mmol/mol (prediabetes threshold); 6.5% = 48 mmol/mol (diabetes threshold); 7.0% = 53 mmol/mol (common treatment target). The formula is: mmol/mol = (HbA1c% - 2.152) / 0.09148.

Iron-deficiency anaemia and vitamin B12 deficiency can falsely elevate HbA1c. Haemoglobin variants (such as HbS in sickle cell trait) can interfere with some testing methods. Recent blood transfusions can lower HbA1c. Pregnancy also affects results. Discuss with your doctor if results seem inconsistent with your glucose meter readings.

Prediabetes means your blood sugar is higher than normal but not yet high enough for a diabetes diagnosis (HbA1c 5.7-6.4%). The CDC estimates 38% of US adults have prediabetes, but only about 19% of them are aware of it. The Diabetes Prevention Program trial showed that lifestyle changes (losing 5-7% of body weight and exercising 150 minutes per week) reduced the risk of progressing to type 2 diabetes by 58%. For adults over 60, the reduction was 71%. Prediabetes is not inevitable progression; many people return to normal HbA1c levels with sustained lifestyle changes. (Sources: CDC, 2022; DPP Research Group, NEJM, 2002.)

The ADA recommends HbA1c testing at least twice a year for people with well-controlled diabetes, and quarterly for those who have changed treatment or are not meeting targets. For people without diabetes, screening should begin at age 35 (or earlier with risk factors such as obesity or family history) and be repeated every 3 years if normal. In the UK, the NHS Health Check programme offers testing for adults aged 40-74 every 5 years. If your result is in the prediabetes range, more frequent monitoring is advisable. (Sources: ADA, 2024; NHS.)

Fasting glucose measures your blood sugar at a single point in time after 8+ hours without eating. HbA1c reflects your average over 2-3 months. Both are used to diagnose diabetes, but they measure different things. You can have a normal fasting glucose but an elevated HbA1c if your blood sugar spikes after meals (postprandial hyperglycaemia). The ADA uses both tests, and a diagnosis can be made with either. Some clinicians prefer HbA1c because it does not require fasting and is less affected by day-to-day variation. (Sources: ADA, 2024; WHO.)

Continuous glucose monitors (CGMs) provide real-time glucose data and calculate the glucose management indicator (GMI), which approximates HbA1c. Some experts argue CGM data is more actionable because it shows patterns, spikes, and variability that HbA1c cannot capture. However, HbA1c remains the standard diagnostic and monitoring test because it has decades of clinical trial data linking it to long-term outcomes. The two are complementary: HbA1c gives the big picture, CGM gives the daily detail. GMI and lab HbA1c can differ by up to 0.5% in individual patients. (Sources: ADA, 2024; Bergenstal et al., Diabetes Care, 2018.)

HbA1c (glycated haemoglobin) measures the percentage of your haemoglobin that has glucose attached to it. Because red blood cells live for approximately 2-3 months, HbA1c reflects your average blood sugar levels over that period. It is a standard test used to diagnose and monitor diabetes. The test does not require fasting and can be done from a simple blood draw. In the US, results are reported as a percentage; in the UK and many other countries, results use mmol/mol. Both scales measure the same thing. (Sources: ADA, 2024; Diabetes UK.)