Medically reviewed by Hemal Patel, PhD, Professor of Anesthesiology at UC San Diego School of Medicine. UCSD profile.
If you hear enough health chatter online, you could be forgiven for thinking every meaningful marker has to sound obscure. HbA1c does not. It has the charisma of an invoice. Still, it remains one of the more clinically useful ways to assess whether glucose regulation has been quietly worsening over time.
That matters because blood sugar problems rarely arrive with a brass band. Long before type 2 diabetes is diagnosed, many people pass through a long stretch of metabolic drift: modest insulin resistance, slightly higher post-meal glucose, creeping central adiposity, a bit less energy, and blood results that seem "not terrible" until they suddenly are. HbA1c helps detect some of that trajectory earlier, although not perfectly.[1][2]
For UK patients, the practical question is simple. What does HbA1c actually tell you, what does it miss, and when is a private result useful rather than merely decorative?
What HbA1c actually measures
HbA1c, or glycated haemoglobin, reflects the percentage of haemoglobin in red blood cells that has glucose attached to it. Because red blood cells circulate for roughly 8 to 12 weeks, the result offers a retrospective view of average glucose exposure across the previous two to three months.[1][3]
That is why HbA1c is different from a fasting glucose result. A fasting glucose test tells you what is happening at a particular moment, after a period without food. HbA1c asks a broader question: how much glucose exposure have your tissues been dealing with lately?
Where the NHS thresholds sit
In UK practice, HbA1c is commonly reported in mmol/mol. Broadly speaking, an HbA1c below 42 mmol/mol is considered below the threshold for non-diabetic hyperglycaemia. A result from 42 to 47 mmol/mol usually falls into the prediabetes range, and 48 mmol/mol or above is one of the criteria used to diagnose diabetes, interpreted alongside symptoms and clinical context.
That framework is sensible and practical. The NHS needs thresholds that are standardised, scalable and well validated. But thresholds are blunt tools. A result of 41 mmol/mol is not an all-clear siren. Nor does 42 mmol/mol mean someone has suddenly crossed into a wholly different biology. Risk tends to rise on a continuum, which is why trends, family history and the wider metabolic picture still matter.
Why clinicians pay attention to HbA1c
HbA1c became widely useful because it does three things reasonably well. First, it is convenient. No fasting is required. Second, it has a strong evidence base for diabetes diagnosis and monitoring. Third, higher HbA1c levels are associated with worse long-term outcomes, including microvascular complications and, in many cohorts, higher cardiovascular risk.[1][4]
It is not simply a diabetes number. It is also a rough proxy for how much glycaemic stress the body has been under. When glucose remains elevated over time, proteins become glycated more readily, oxidative stress rises, vascular injury becomes more likely, and the broader cardiometabolic picture often starts to look less forgiving.
None of this means you should become emotionally attached to the decimal places. It does mean HbA1c deserves a place in any serious prevention conversation.
What HbA1c can miss
This is the part often skipped by both overconfident marketers and overconfident sceptics. HbA1c is useful, but it can absolutely miss things.
Because it is an average, it can flatten out glucose variability. Someone with frequent post-meal spikes and crashes may still produce an HbA1c that looks only mildly elevated, or even normal. Continuous glucose monitoring studies in healthy adults show that glucose excursions happen more often than many people assume, even outside diagnosed diabetes.[3]
HbA1c can also be distorted when red blood cell lifespan changes. Anaemia, recent blood loss, haemoglobin variants, pregnancy, kidney disease, or some inflammatory and haematological conditions can all affect interpretation. In other words, the number is informative, but not infallible. Biology remains impolite.
When private testing can add useful context
The NHS is built to diagnose, treat and risk-stratify at population scale. It is not built to indulge every mildly prevention-minded person who wants an unusually detailed baseline. That is understandable. It also leaves a gap for people who are not ill, but are not entirely reassured either.
Private biomarker testing may be useful when:
- there is a family history of type 2 diabetes or early cardiovascular disease,
- weight, waist circumference or triglycerides are drifting up,
- energy, appetite regulation or recovery feel less stable than before,
- you want to track the metabolic effect of lifestyle changes before a formal diagnosis exists.
That is also why our guide to preventative tests the NHS does not routinely offer resonates with so many patients. The issue is not that the NHS is negligent. It is that early prevention often sits awkwardly between public-health pragmatism and individual curiosity.
Why HbA1c belongs in a broader metabolic picture
HbA1c should not be interpreted in isolation. A meaningful metabolic picture also includes blood pressure, triglycerides, HDL cholesterol, body composition, sleep quality, activity patterns, alcohol intake, stress load and family history. In some cases, fasting insulin, fasting glucose or continuous glucose monitoring may provide further context.
That broader view matters for MeScreen patients because energy regulation, inflammatory tone and metabolic resilience do not live in separate rooms. Mitochondrial function, glucose handling and cardiovascular risk overlap in ways that are biologically dull but clinically important. Resources such as our mitochondrial health hub and scientific studies page are useful precisely because they keep single markers in proportion.
What to do if your HbA1c is edging up
If HbA1c is creeping into the prediabetes range, the answer is not panic. It is usually a fairly unromantic review of basics done well and for long enough to matter. Weight loss where appropriate, resistance training, brisk walking after meals, better sleep, more fibre, less ultra-processed food, and a more stable eating pattern remain more effective than most supplement folklore.
The goal is not perfection. It is reducing glycaemic load and improving insulin sensitivity before the pattern hardens. Then repeat the test after enough time has passed to show whether the trend has actually moved.
The sober bottom line for UK patients
HbA1c is worth taking seriously because it is simple, well validated and genuinely useful. It helps identify long-view blood sugar risk without needing a fasting sample, and it fits sensibly within NHS practice. But it is still only one marker. It can miss early dysregulation, it can be skewed by red blood cell issues, and it should always be interpreted alongside the rest of the person.
If you want a more complete baseline, private testing can add value, provided the aim is clarity rather than theatre. Better prevention usually starts the same way: less hype, more context, and a willingness to notice slow changes before they become expensive ones.
Medically reviewed by Hemal Patel, PhD
Professor of Anesthesiology at UC San Diego School of Medicine, with research interests in mitochondrial biology, caveolin signalling and cellular bioenergetics.
Read Hemal Patel's MeScreen reviewer profile ยท Verify on UCSD Profiles
Better prevention starts before symptoms do.
If you want a deeper view of metabolic and cellular health, start with testing that is clinically grounded, interpretable and actually useful for next-step decisions.
Frequently asked questions
What does HbA1c actually measure?
HbA1c estimates the proportion of haemoglobin in red blood cells that has glucose attached to it. Because red blood cells circulate for roughly 2 to 3 months, the result gives a longer-view estimate of average glucose exposure rather than a single moment in time.
What HbA1c level counts as prediabetes in the UK?
In UK practice, an HbA1c of 42 to 47 mmol/mol is generally treated as non-diabetic hyperglycaemia, often called prediabetes. A result of 48 mmol/mol or above is one of the thresholds used to diagnose diabetes, interpreted alongside clinical context.
Can HbA1c miss blood sugar problems?
Yes. HbA1c is useful, but it can miss early glucose spikes and can be affected by conditions that alter red blood cell turnover, including some anaemias, recent blood loss, haemoglobin variants, pregnancy, or kidney disease.
Should HbA1c be interpreted on its own?
No. HbA1c is most useful alongside waist circumference, blood pressure, triglycerides, activity levels, sleep, family history, and where relevant fasting glucose or continuous glucose monitoring.
References
- International Expert Committee. International Expert Committee report on the role of the A1C assay in the diagnosis of diabetes. Diabetes Care. 2009;32(7):1327-1334. doi:10.2337/dc09-9033.
- Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008;31(8):1473-1478. doi:10.2337/dc08-0545.
- Shah VN, DuBose SN, Li Z, et al. Continuous glucose monitoring profiles in healthy nondiabetic participants: a multicenter prospective study. J Clin Endocrinol Metab. 2019;104(10):4356-4364. doi:10.1210/jc.2018-02763.
- Selvin E, Steffes MW, Zhu H, et al. Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults. N Engl J Med. 2010;362(9):800-811. doi:10.1056/NEJMoa0908359.