HbA1c is not included in a full blood count (FBC) — these are two entirely separate blood tests that measure different things. A full blood count, sometimes called a CBC, assesses the cellular components of your blood, such as red cells, white cells, and platelets. HbA1c, or glycated haemoglobin, measures your average blood glucose over the past two to three months and must be requested separately by your GP. Understanding the difference between these tests helps you know exactly what has — and has not — been checked when you receive your results.

What Is a Full Blood Count and What Does It Measure?

A full blood count (FBC) is a haematological test measuring red cells, white cells, platelets, haemoglobin, haematocrit, and MCV; it does not measure blood glucose, hormones, or metabolic markers.

A full blood count (FBC) — sometimes referred to in other countries as a complete blood count (CBC) — is one of the most commonly requested blood tests in the NHS. It provides a broad overview of the cellular components of your blood and is used to help diagnose, monitor, or screen for a wide range of conditions.

The FBC measures several key parameters, including:

• Red blood cells (RBCs): Their number, size, and haemoglobin content, which reflects the blood's oxygen-carrying capacity

• White blood cells (WBCs): Total count and differential (the breakdown of different white cell types), which helps assess immune function and detect infection or haematological conditions

• Platelets: Small cell fragments essential for blood clotting

• Haemoglobin (Hb): The protein within red cells that carries oxygen

• Haematocrit (PCV): The proportion of blood volume made up of red cells

• Mean corpuscular volume (MCV): The average size of red blood cells, useful in classifying anaemia

The FBC is a purely haematological test — it evaluates the physical and quantitative characteristics of blood cells. It does not measure blood glucose levels, hormones, kidney function markers, or metabolic indicators. This distinction is important because patients sometimes assume that a routine blood test covers all possible parameters.

In clinical practice, an FBC is often ordered alongside other panels — such as a metabolic profile or liver function tests — but each panel serves a distinct diagnostic purpose. It is worth noting that the specific parameters reported and the reference intervals used may vary between NHS laboratories; your results will always be interpreted against the reference ranges used by the laboratory that processed your sample.

What Is HbA1c and Why Is It Tested Separately?

HbA1c measures the proportion of haemoglobin glycated by glucose over 90–120 days and is not part of the FBC; it must be specifically requested and is used to diagnose and monitor diabetes.

HbA1c, or glycated haemoglobin, is a blood test that measures the average blood glucose level over the preceding two to three months. It works by detecting the proportion of haemoglobin molecules that have glucose permanently attached to them — a process called glycation. Because red blood cells have a lifespan of approximately 90–120 days, HbA1c provides a reliable long-term picture of blood sugar control, unlike a fasting glucose test, which only reflects a single point in time.

To be clear: HbA1c is not included in a full blood count. Although both tests involve blood and both reference haemoglobin, they measure entirely different things. The FBC measures the quantity and characteristics of haemoglobin within red cells; HbA1c measures the degree to which that haemoglobin has been chemically modified by glucose. They are processed using different laboratory methods and serve different clinical purposes.

In the UK, HbA1c is used by NHS clinicians to:

• Diagnose type 2 diabetes: A result of 48 mmol/mol (6.5%) or above on two separate occasions (in the absence of symptoms) is diagnostic

• Identify non-diabetic hyperglycaemia (pre-diabetes): Results between 42–47 mmol/mol (6.0–6.4%) indicate an increased risk of developing type 2 diabetes

• Monitor glycaemic control in people already diagnosed with type 1 or type 2 diabetes

NICE guidelines (NG28 and NG17) recommend HbA1c as the preferred diagnostic and monitoring tool for type 2 diabetes in most adults. For diagnosis, HbA1c must be measured using an IFCC-standardised, quality-assured laboratory method — point-of-care (finger-prick) HbA1c devices should not be used for diagnostic purposes.

HbA1c should not be used to diagnose diabetes in the following situations (per NICE NG28, NG17, and NG3):

• Children and young people

• Adults with suspected type 1 diabetes

• Pregnancy or when gestational diabetes is being evaluated (an oral glucose tolerance test, or OGTT, is used instead)

• People who have been acutely unwell or whose symptoms have been present for fewer than two months

• People taking medications that can cause rapid rises in blood glucose (for example, high-dose corticosteroids)

• Conditions that alter red blood cell lifespan or haemoglobin structure, including haemoglobinopathies (such as sickle cell trait), haemolytic anaemia, iron deficiency anaemia, recent blood transfusion, or advanced chronic kidney disease (CKD)

In these circumstances, a fasting plasma glucose test or OGTT may be used instead. HbA1c must be specifically requested by your GP or clinician — it will not appear automatically on a standard FBC request. If you are concerned about your blood sugar levels, speak to your GP, who can arrange this test separately.

When Your GP or NHS Clinician May Order Both Tests

A GP may request both FBC and HbA1c together when investigating fatigue, managing known diabetes with haematological conditions, or conducting a broad assessment of unexplained symptoms.

Although HbA1c and FBC are distinct tests, there are many clinical scenarios in which a GP or hospital clinician may request both at the same time. This is common practice when a patient presents with symptoms or risk factors that could involve both haematological and metabolic concerns.

For example, a clinician might order both tests when:

• Assessing fatigue or tiredness: Anaemia (detected by FBC) and poorly controlled diabetes (reflected in HbA1c) can both cause significant fatigue, and distinguishing between them — or identifying both — requires separate testing

• Conducting an NHS Health Check: This programme, offered to adults aged 40–74 in England, includes cardiovascular risk assessment and cholesterol testing. Where a diabetes risk assessment indicates raised risk, HbA1c or fasting plasma glucose may be offered. An FBC is not a standard component of the NHS Health Check, but may be requested separately if clinically indicated

• Managing a patient with known type 2 diabetes: Certain conditions that alter red blood cell lifespan — such as haemolysis, iron deficiency, haemoglobinopathies, recent blood transfusion, or treatment with erythropoietin (EPO) — can affect the reliability of HbA1c results. An FBC helps the clinician interpret the glycated haemoglobin result in the correct haematological context. Where HbA1c is considered unreliable, fasting plasma glucose or an OGTT may be used instead

• Investigating unexplained weight loss or general malaise: A broad panel including both tests helps rule out multiple causes simultaneously

Your GP will consider your full clinical picture when deciding which combination of tests is most appropriate for you.

Understanding Your Blood Test Results in the UK

An FBC does not check blood sugar; if HbA1c was not specifically requested, your glucose levels have not been tested, and you should ask your GP surgery which tests were included.

Receiving blood test results can sometimes feel confusing, particularly when multiple tests are ordered at once or when results are shared via an NHS online portal such as the NHS App or Patient Access without immediate explanation. Understanding what each test covers — and what it does not — can help you engage more confidently with your healthcare team.

If you have had a full blood count and are wondering whether your blood sugar has been checked, the answer is no — unless HbA1c or a fasting glucose test was specifically requested at the same time. Always check your test request form or ask your GP surgery which tests were included in your blood draw.

Typical reference ranges used in the UK include:

• Haemoglobin (FBC): Approximately 130–180 g/L in men; 115–165 g/L in women. Reference intervals vary between NHS laboratories — always refer to the ranges provided on your own results

• HbA1c — normal: Below 42 mmol/mol (6.0%)

• HbA1c — non-diabetic hyperglycaemia (pre-diabetes): 42–47 mmol/mol (6.0–6.4%)

• HbA1c — diabetes: 48 mmol/mol (6.5%) or above

If your results fall outside the normal range, your GP will usually contact you to discuss next steps. You should contact your GP promptly if you experience:

• Unexplained fatigue, breathlessness, or pallor (which may suggest anaemia)

• Increased thirst, frequent urination, or unexplained weight loss (which may suggest elevated blood glucose)

• Any result flagged as abnormal on your patient portal

Important — suspected type 1 diabetes: If you or your child experience symptoms such as excessive thirst, frequent urination, unexplained weight loss, abdominal pain, vomiting, drowsiness, or breath that smells of acetone, seek same-day medical assessment. Children and young people with suspected type 1 diabetes require urgent same-day referral, in line with NICE guidance (NG17).

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Never adjust medications or make significant lifestyle changes based solely on online results without speaking to a clinician first. NHS and NICE both emphasise that blood test results should always be interpreted in the context of your individual health history and symptoms.

Frequently Asked Questions