HbA1c 6% (42 mmol/mol) corresponds to an estimated average blood glucose of approximately 7.0 mmol/L over the preceding two to three months. Far from being a reassuringly normal result, this level falls within the non-diabetic hyperglycaemia range as defined by NICE — indicating an elevated risk of developing type 2 diabetes. Understanding what this figure means, how HbA1c reflects longer-term blood sugar control, and what steps to take next is essential for anyone who has received this result. This article explains the clinical significance of an HbA1c of 6, relevant NHS and NICE guidance, and when to seek further advice from your GP.

What an HbA1c of 6 Means for Your Average Blood Sugar

An HbA1c of 6% (42 mmol/mol) corresponds to an estimated average blood glucose of approximately 7.0 mmol/L and falls within the NICE-defined non-diabetic hyperglycaemia range, indicating elevated risk of type 2 diabetes rather than a normal result.

An HbA1c of 6% (42 mmol/mol in the standardised IFCC units used in the UK) corresponds to an estimated average blood glucose of approximately 7.0 mmol/L over the preceding two to three months. This estimate is derived from population data (the ADAG study) and is not a figure routinely reported by UK laboratories alongside your HbA1c result.

In the UK, HbA1c results are reported in mmol/mol, though the older percentage format is still widely referenced. It is important to understand that an HbA1c of 42 mmol/mol (6.0%) falls within — not below — the range that NICE classifies as non-diabetic hyperglycaemia (high risk), defined as 42–47 mmol/mol. This means a result at this level is not diagnostic of type 2 diabetes, but it does indicate an elevated risk of developing it. It should not be dismissed as entirely normal.

NICE guidance (PH38) recommends that people with non-diabetic hyperglycaemia are offered structured lifestyle support and have their HbA1c rechecked at least annually. If you have received this result, your GP or practice nurse should discuss what it means for you personally, particularly if you have additional risk factors such as overweight or obesity, a family history of type 2 diabetes, or cardiovascular disease.

It is also important to understand that the estimated average glucose derived from HbA1c is a mathematical approximation, not a direct measurement of blood sugar at any single point in time. Individual variation means that two people with the same HbA1c may have quite different day-to-day glucose patterns.

How HbA1c Reflects Blood Glucose Levels Over Time

HbA1c measures the proportion of glycated haemoglobin in red blood cells, providing a time-weighted average of blood glucose over the preceding 90–120 days, with the most recent four to six weeks contributing most to the result.

HbA1c — or glycated haemoglobin — is formed when glucose in the bloodstream binds irreversibly to haemoglobin, the protein found inside red blood cells. Because red blood cells have a lifespan of approximately 90 to 120 days, the proportion of haemoglobin that has become glycated provides a reliable indicator of average blood glucose control over the preceding two to three months. It is worth noting that HbA1c reflects a time-weighted average, with the most recent four to six weeks contributing more to the result than earlier weeks.

HbA1c complements, rather than replaces, plasma glucose testing; each test serves a different clinical purpose. A single fasting glucose measurement reflects blood sugar at one moment in time, whereas HbA1c provides a longer-term picture of glycaemic control.

The relationship between HbA1c and estimated average glucose (eAG) is broadly linear, based on the ADAG study:

• HbA1c 6% (42 mmol/mol) ≈ estimated average glucose of 7.0 mmol/L

• HbA1c 7% (53 mmol/mol) ≈ estimated average glucose of 8.6 mmol/L

• HbA1c 8% (64 mmol/mol) ≈ estimated average glucose of 10.2 mmol/L

These conversions are population-based estimates and may not perfectly reflect every individual's physiology. Importantly, HbA1c does not capture glucose variability — it cannot distinguish between someone who maintains a steady blood sugar of 7.0 mmol/L and someone who swings between hypoglycaemic and hyperglycaemic episodes but averages the same figure. For this reason, clinicians may use continuous glucose monitoring or self-monitored blood glucose readings alongside HbA1c to gain a fuller picture of glycaemic control (NICE NG28).

What NHS and NICE Guidelines Say About HbA1c Targets

NICE classifies HbA1c below 42 mmol/mol as normal, 42–47 mmol/mol as non-diabetic hyperglycaemia requiring lifestyle intervention, and 48 mmol/mol or above as diagnostic of type 2 diabetes on confirmatory testing.

According to NICE guidelines and NHS clinical practice, HbA1c thresholds are used to classify glycaemic status and guide clinical decision-making:

• Below 42 mmol/mol (6.0%): Generally considered within the normal range for adults without diabetes.

• 42–47 mmol/mol (6.0–6.4%): Classified as non-diabetic hyperglycaemia (high risk) — sometimes referred to as 'pre-diabetes' — indicating an elevated risk of developing type 2 diabetes. NICE (PH38) recommends structured lifestyle interventions and at least annual HbA1c monitoring for people in this range.

• 48 mmol/mol (6.5%) or above: Diagnostic of type 2 diabetes when confirmed on a repeat test in the absence of symptoms, or on a single test in the presence of typical symptoms.

For people already diagnosed with type 2 diabetes, NICE (NG28) recommends an individualised HbA1c target — typically 48 mmol/mol (6.5%) for those managed by lifestyle or a single non-hypoglycaemic drug, or 53 mmol/mol (7%) for those on more complex regimens or at higher risk of hypoglycaemia. For type 1 diabetes, NICE (NG17) recommends aiming for an HbA1c of 48 mmol/mol (6.5%) or below if this can be achieved safely without problematic hypoglycaemia.

NICE emphasises shared decision-making, taking into account the individual's circumstances, treatment burden, and quality of life. Overly aggressive lowering of HbA1c — particularly in older adults or those with significant comorbidities — can increase the risk of hypoglycaemia and is not always clinically appropriate.

Important limitations of HbA1c for diagnosis NICE guidance specifies that HbA1c should not be used to diagnose diabetes in the following situations:

• Pregnancy (including for the diagnosis of gestational diabetes — see NICE NG3)

• Children and young people

• Suspected type 1 diabetes or acute-onset hyperglycaemia

• Conditions that alter red blood cell turnover or haemoglobin structure (such as haemolytic anaemia, haemoglobin variants, or recent blood transfusion)

In these circumstances, plasma glucose testing (fasting glucose or oral glucose tolerance test) should be used instead.

Factors That Can Affect Your HbA1c Reading

Several conditions — including haemolytic anaemia, iron deficiency, haemoglobin variants, and pregnancy — can falsely lower or raise HbA1c, meaning plasma glucose or alternative testing may be needed for accurate assessment.

While HbA1c is a robust and widely validated test, several physiological and clinical factors can influence the result, sometimes leading to readings that do not accurately reflect true average blood glucose levels. Being aware of these factors helps both patients and clinicians interpret results more accurately. Where such conditions are present, NICE recommends considering alternative measures such as plasma glucose, oral glucose tolerance testing, fructosamine, or continuous glucose monitoring.

Conditions that may falsely lower HbA1c:

• Haemolytic anaemia (increased red blood cell turnover reduces the time available for glycation)

• Recent blood transfusion

• Haemoglobin variants such as sickle cell trait or haemoglobin C disease

• Pregnancy (particularly in the second and third trimesters)

• Advanced chronic kidney disease with anaemia or erythropoietin therapy (shortened red blood cell survival)

Conditions that may falsely raise HbA1c:

• Iron deficiency anaemia (before treatment)

• Vitamin B12 or folate deficiency

• Splenectomy (prolonged red blood cell survival)

• Chronic kidney disease (uraemia can interfere with the assay, though the effect is bidirectional depending on the method used and the degree of renal impairment)

Certain medications can also indirectly affect HbA1c by altering blood glucose levels. Corticosteroids such as prednisolone are well known to raise blood glucose and may therefore elevate HbA1c with prolonged use. Conversely, glucose-lowering agents, when used appropriately, will reduce HbA1c as intended.

Ethnicity may also play a modest role; some studies suggest that people of African-Caribbean or South Asian heritage may have slightly higher HbA1c values at equivalent blood glucose levels, though the clinical significance of this remains an area of ongoing research. If your clinician suspects that a haematological condition may be affecting your result, they will discuss appropriate alternative testing with you.

When to Speak to Your GP About Your HbA1c Result

Anyone with an HbA1c of 42 mmol/mol (6.0%) should discuss the result with their GP, who can assess individual risk, refer to a structured lifestyle programme, and arrange at least annual monitoring as recommended by NICE (PH38).

An HbA1c of 42 mmol/mol (6.0%) falls within the non-diabetic hyperglycaemia (high risk) range as defined by NICE (PH38). It is important to discuss this result with your GP or practice nurse, who can explain what it means for your individual risk, offer or refer you to a structured lifestyle programme, and arrange at least annual HbA1c monitoring going forward.

Contact your GP promptly if:

• Your HbA1c has risen compared to a previous result, even if it remains below the diabetes threshold

• You have additional risk factors for type 2 diabetes, such as overweight or obesity, a family history of type 2 diabetes, or a history of gestational diabetes

• You have been prescribed a new medication (such as a corticosteroid or antipsychotic) that may affect blood glucose

Seek urgent same-day medical assessment if you experience:

• Marked increase in thirst or urination, particularly with signs of dehydration

• Rapid or unexplained weight loss

• Vomiting, abdominal pain, or drowsiness alongside symptoms of high blood sugar

• Confusion or reduced consciousness

• Positive ketone reading on a home test

These symptoms may indicate a more acute problem requiring prompt assessment and should not be managed by waiting for a routine appointment.

For people already diagnosed with diabetes who are achieving an HbA1c of 42 mmol/mol (6.0%) whilst taking glucose-lowering medication — particularly insulin or sulphonylureas — it is equally important to discuss this with your GP. An HbA1c lower than expected in someone on such treatments may indicate a risk of hypoglycaemia, which carries its own serious health risks. If you experience or suspect side effects from any medication, you can report these directly to the MHRA via the Yellow Card scheme (yellowcard.mhra.gov.uk).

Monitoring frequency NICE recommends the following HbA1c monitoring intervals:

• Non-diabetic hyperglycaemia (high risk): At least annually (NICE PH38)

• Type 2 diabetes: Every three to six months until stable, then every six months (NICE NG28)

• Type 1 diabetes: As agreed with your diabetes care team, typically every three to six months (NICE NG17)

Routine annual HbA1c testing is not recommended for adults at low risk with no diabetes or risk factors. Attending scheduled reviews and maintaining an open dialogue with your healthcare team is the most effective way to protect your long-term metabolic health.

Frequently Asked Questions