Can COVID increase HbA1c? Evidence suggests it can. COVID-19 infection has been linked to disruptions in blood glucose regulation that may raise HbA1c — the key marker reflecting average blood sugar control over the preceding two to three months. Whether through direct effects on insulin-producing cells, the body's intense inflammatory response, stress hormone release, or corticosteroid treatment, SARS-CoV-2 can affect glycaemic control in meaningful ways. This article explores the mechanisms behind COVID-related HbA1c changes, what the research shows, who is most at risk, when to seek testing, and how raised HbA1c is managed under NHS guidance.

How COVID-19 May Affect Blood Sugar and HbA1c Levels

COVID-19 raises blood sugar through insulin resistance driven by inflammatory cytokines, stress hormone-induced hepatic glucose release, and corticosteroid use — effects that can cumulatively elevate HbA1c if sustained over several weeks.

There is growing evidence that COVID-19 infection can disrupt glucose metabolism in ways that may raise HbA1c levels — a key marker of average blood sugar control over the preceding two to three months. Understanding why this happens requires a brief look at how the SARS-CoV-2 virus interacts with the body at a cellular level.

The virus enters human cells primarily via the ACE2 receptor, which is expressed in multiple tissues including the lungs. Some studies have reported ACE2 expression in pancreatic beta cells, raising the possibility that direct viral effects could impair insulin secretion; however, the evidence for direct beta-cell infection and cytotoxicity in humans remains mixed and is still under investigation. Additionally, the intense inflammatory response triggered by COVID-19 — characterised by raised cytokines such as interleukin-6 and tumour necrosis factor-alpha — promotes insulin resistance, meaning the body's cells become less responsive to insulin even when it is present.

Beyond any direct viral effects, the physiological stress of serious illness causes the adrenal glands to release cortisol and adrenaline. These stress hormones stimulate the liver to release stored glucose (glycogenolysis) and produce new glucose (gluconeogenesis), further pushing blood sugar levels upward. If this persists over several weeks — as can occur in prolonged or severe COVID-19 — the cumulative effect may be reflected in a measurably higher HbA1c reading. It is worth noting that brief spikes in blood glucose lasting only a few days are unlikely to materially alter HbA1c, as the test reflects average glycaemia over approximately 8–12 weeks.

It is also worth noting that reduced physical activity, changes in diet during illness, and the use of corticosteroids such as dexamethasone (commonly prescribed in hospitalised COVID-19 patients, and listed in the dexamethasone Summary of Product Characteristics as a cause of hyperglycaemia) can independently raise blood glucose and contribute to an elevated HbA1c. In line with Joint British Diabetes Societies (JBDS) guidance on steroid-induced hyperglycaemia, these effects typically improve after the steroid dose is tapered or stopped, though monitoring remains important. These factors often act together, making the overall impact on glycaemic control more pronounced.

What the Research Says About COVID-19 and HbA1c Changes

Population-based studies show a statistically higher risk of new diabetes diagnosis within 12 months of COVID-19 infection, though confounders including pre-existing pre-diabetes and detection bias mean causality is not fully established.

Several peer-reviewed studies and clinical observations have explored the relationship between COVID-19 and changes in HbA1c. The evidence, while still evolving, suggests a meaningful association — particularly in individuals who experienced moderate to severe illness.

A notable finding from multiple studies is the emergence of new-onset diabetes following COVID-19 infection. Research published in journals including The Lancet Diabetes & Endocrinology and large UK and international population-based cohort analyses has documented cases where individuals with no prior history of diabetes developed hyperglycaemia and raised HbA1c in the weeks to months following infection. Diabetes UK and international diabetes bodies have acknowledged this phenomenon, though the precise mechanisms and long-term trajectory remain under investigation.

Data from large population-based studies suggest that people who contracted COVID-19 had a statistically higher risk of receiving a new diabetes diagnosis within 12 months compared with those who had not been infected. However, it is important to note that causality is not fully established in all cases. Several confounders should be considered: some individuals may have had undiagnosed pre-diabetes prior to infection, with COVID-19 acting as a trigger that accelerated progression rather than being the sole cause; increased healthcare contact and testing following COVID-19 may lead to detection of previously unrecognised diabetes (detection bias); and corticosteroid treatment during hospitalisation is itself a recognised cause of hyperglycaemia.

For those with pre-existing type 2 diabetes, studies have shown that COVID-19 illness can destabilise previously well-controlled blood glucose, resulting in HbA1c values rising above baseline. Conversely, some research has noted that HbA1c changes may partially normalise over time once the acute illness resolves and lifestyle factors stabilise — though this is not universal. The overall picture supports the view that COVID-19 can increase HbA1c, at least transiently, and in some cases more persistently.

Who Is Most at Risk of HbA1c Rises After COVID-19

People with pre-existing type 2 diabetes, obesity, or cardiovascular disease, those hospitalised with COVID-19, older adults, and individuals of South Asian or Black African heritage face the greatest risk of COVID-related HbA1c rises.

Not everyone who contracts COVID-19 will experience a significant change in their HbA1c. Certain groups, however, appear to be at considerably higher risk of developing raised blood sugar levels or worsening glycaemic control following infection.

Those at greatest risk include:

• People with pre-existing type 2 diabetes or impaired glucose regulation (pre-diabetes), whose glycaemic control may be more vulnerable to the metabolic disruption caused by infection

• Individuals who were hospitalised with COVID-19 or required intensive care, as severe illness and corticosteroid treatment are strongly associated with hyperglycaemia

• People with obesity (BMI ≥30 kg/m²), as adipose tissue contributes to baseline insulin resistance, which COVID-19 may exacerbate

• Those with cardiovascular disease, hypertension, or metabolic syndrome, conditions that share pathophysiological pathways with impaired glucose metabolism

• Older adults, who may have reduced pancreatic reserve and are more susceptible to stress-induced hyperglycaemia

• Individuals of South Asian, Black African, or Black Caribbean heritage, who have a higher background risk of type 2 diabetes in UK populations and may therefore be more susceptible to COVID-related glycaemic disruption

People who experienced long COVID — persistent symptoms lasting beyond 12 weeks, as described in NICE guideline NG191 — also appear to be at elevated risk. Ongoing fatigue, reduced activity levels, and continued low-grade inflammation in long COVID may sustain the conditions that drive raised blood glucose over a prolonged period, though the evidence in this specific area continues to develop.

It is equally important to recognise that some individuals with no known risk factors have developed new-onset hyperglycaemia following COVID-19. This underscores the importance of clinical vigilance across a broad patient population, not only in those with established metabolic risk.

A note on pregnancy and younger people: Pregnant women and children or young people who develop symptoms of hyperglycaemia following COVID-19 require separate assessment pathways and diagnostic criteria. HbA1c is not appropriate for diagnosing diabetes in pregnancy; plasma glucose-based testing should be used instead. These groups should be referred promptly to the appropriate specialist service.

When to Get Your HbA1c Checked After a COVID-19 Infection

People with pre-existing diabetes or pre-diabetes should arrange an HbA1c check two to three months after recovering from COVID-19; those developing symptoms of hyperglycaemia should contact their GP promptly.

Given the potential for COVID-19 to affect blood glucose regulation, knowing when to seek an HbA1c test is an important aspect of post-infection care. Current NHS and NICE guidance does not mandate universal HbA1c screening following COVID-19 for the general population, but clinical judgement and individual risk factors should guide testing decisions.

Seek urgent or same-day medical assessment — do not wait for a routine appointment — if you develop any of the following after a COVID-19 infection:

• Severe or rapidly worsening thirst and very frequent urination

• Vomiting, abdominal pain, or rapid/deep breathing

• Confusion, drowsiness, or signs of dehydration

• Blood glucose readings that are very high on a home monitor

These symptoms may indicate diabetic ketoacidosis (DKA) or hyperosmolar hyperglycaemic state (HHS), both of which are medical emergencies. Call 999 or go to your nearest A&E if you are concerned. Further information is available on the NHS website.

You should consider speaking to your GP about an HbA1c test if, following a COVID-19 infection, you experience any of the following:

• Persistent or unexplained excessive thirst or frequent urination (without the severe features above)

• Unusual fatigue that does not improve with rest

• Unintentional weight loss

• Blurred vision or recurrent infections (e.g., thrush, urinary tract infections)

• Blood glucose readings above the normal range if you have a home monitor

For individuals with pre-existing type 2 diabetes or pre-diabetes, it is advisable to arrange an HbA1c check approximately two to three months after recovering from COVID-19, as this allows sufficient time for the test to reflect any sustained changes in blood glucose control during and after the illness. Those who were hospitalised or required corticosteroid treatment should discuss earlier or more frequent monitoring with their diabetes care team.

For people with no prior history of diabetes, a one-off HbA1c test is reasonable if symptoms suggestive of hyperglycaemia develop, or if you fall into one of the higher-risk groups outlined above. Your GP can arrange this as a routine blood test.

Important limitations of HbA1c testing: HbA1c is not suitable for diagnosing diabetes in all circumstances. It should not be used in pregnancy, in children and young people, where type 1 diabetes is suspected, or in people with conditions that affect red blood cell turnover (such as haemoglobinopathies, haemolytic anaemia, or following a recent blood transfusion). In these situations, plasma glucose-based tests are used instead, as set out in NICE guideline NG28. Your GP will advise on the most appropriate test for your circumstances.

Early identification of raised HbA1c allows timely intervention, which is associated with significantly better long-term outcomes in preventing progression to type 2 diabetes or its complications.

Managing Raised HbA1c Following COVID-19: NHS Guidance

Management follows NICE NG28 thresholds: pre-diabetes (42–47 mmol/mol) warrants NHS Diabetes Prevention Programme referral, while confirmed type 2 diabetes (≥48 mmol/mol) is treated with lifestyle modification and, if needed, metformin or an SGLT2 inhibitor.

If a raised HbA1c is identified following COVID-19 infection, management will depend on the degree of elevation, the presence of symptoms, and whether a diagnosis of pre-diabetes or type 2 diabetes is confirmed. NHS and NICE guidelines provide a clear framework for this.

HbA1c interpretation thresholds (NICE NG28 and NHS/UKHSA definitions):

• Below 42 mmol/mol — normal range

• 42–47 mmol/mol — non-diabetic hyperglycaemia (pre-diabetes); lifestyle intervention recommended

• 48 mmol/mol and above — indicative of type 2 diabetes (requires confirmatory testing if the person is asymptomatic)

For those with pre-diabetes following COVID-19, NICE recommends referral to the NHS Diabetes Prevention Programme (NHS DPP), a structured, evidence-based intervention focusing on dietary changes, increased physical activity, and weight management. NHS evaluations indicate this programme reduces the risk of progression to type 2 diabetes, though individual outcomes vary.

For those with a new or worsening type 2 diabetes diagnosis, NICE guideline NG28 supports a stepwise approach beginning with lifestyle modification, followed by pharmacological therapy if targets are not met. Metformin remains the first-line medication of choice in most cases, given its established safety profile, low cost, and evidence base. For people with established cardiovascular disease, chronic kidney disease, or heart failure, updated NICE guidance and relevant technology appraisals support early consideration of an SGLT2 inhibitor (such as empagliflozin or dapagliflozin), given the additional cardiorenal benefits these medicines offer. Blood pressure and lipid management should also be reviewed, as cardiovascular risk is elevated in this group.

If type 1 diabetes is suspected — for example, in a younger person, someone with rapid symptom onset, or someone with significant weight loss — urgent same-day specialist assessment should be arranged, as management differs substantially from type 2 diabetes.

It is worth noting that in some individuals, HbA1c may improve as recovery from COVID-19 progresses and lifestyle factors normalise. However, this should not be assumed — ongoing monitoring is essential. Patients should be supported to:

• Adopt a balanced, lower-glycaemic diet rich in vegetables, wholegrains, and lean protein

• Gradually increase physical activity in line with post-COVID recovery capacity

• Attend regular follow-up appointments with their GP or diabetes nurse

If you are taking any medicines and think you may be experiencing side effects, you can report these to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

If you are concerned about your blood sugar levels following COVID-19, contact your GP practice. Early action is the most effective way to protect your long-term metabolic health.

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