• Hannah

What is a full blood count?

If you are experiencing symptoms of illness, your GP may take a sample of your blood to conduct a Full Blood Count. A full blood count or complete blood count (CBC) is a blood test used to evaluate your overall health. It can also be used to detect a range of disorders including anaemia and infection. You may have had a few blood tests in the past. Do you know exactly what your blood is tested for? Are you feeling unwell and wondering what a full blood count is designed to pick up in testing? In this article, we explain what a full blood count is and the reasons why your doctor might suggest you have full bloods done.

What does a full blood count measure?

There are a number of components that together make the substance that is blood. Your blood has a certain number of certain types of "building blocks", making healthy blood. If the levels are abnormal to any of these building blocks, then it could be an indication of an illness or an infection. A full blood count measures these levels to make sure that there are no indicators of ill health. A complete blood count test measures several building blocks or components and features of your blood. These are included below:

Red blood cells and haemoglobin

Red blood cells carry oxygen through your body. They also remove carbon dioxide and transport it to your lungs in order for you to expel or exhale it. Red blood cells live for around 120 days, and then they die. However, they replenish and are re-made by the body. So if you're feeling fatigued or weak, this may be a sign of too little red blood cells in your system. This condition is called anaemia. You still need oxygen, so it means your red blood cells are working overtime to move oxygen around the body. The test also monitors your red blood cell to plasma ratio.

White blood cells

Your white blood cells are small in number, but they pack a big punch. They account for only 1% of your blood, but they are responsible for protecting you against illness and disease. A white blood cell's job is to flow through your body and fight viruses and bacteria. Unfortunately, white blood cells have an even shorter lifespan than red blood cells, so your body is always (or should always be) making new ones. A full blood count takes note of whether you have a normal number of white blood cells in your system. A high white blood cell count can indicate that you have been fighting an infection. If your white blood cell count is low, your immune system is weakened and this could be caused by a number of conditions.


Platelets are the tiny blood cells that help your body form blood clots and stop bleeding. If a blood vessel is damaged, your platelets rush to fix the damage and create a clot. If you have a low platelet count, it could be a sign of a number of different conditions or a side effect of medications.

Abnormal increases or decreases in cell counts revealed in a full blood count test can indicate that you have an underlying medical condition. The results of this test can help your doctor to narrow down conditions until they are able to obtain the cause of your symptoms. 

Why would I need a full blood count?

A complete or full blood count is a common blood test and is conducted by your GP for a variety of different reasons. These could include:

  • A review of your overall health. Your doctor may recommend a complete blood count as part of a routine medical examination to monitor your health. They may also conduct one as part of an annual health check to screen for a variety of different disorders, such as anaemia or a more serious illness.

  • A test to diagnose a specific medical condition. Your GP may suggest a complete blood count if you are experiencing specific symptoms. If you are weak, fatigued, have bruising, bleed or inflammation, for example, then your GP may use a full blood count to diagnose the cause of these symptoms. In addition, this test can also detect any sign of infection.

  • Monitoring a medical condition you already have. If you have been diagnosed with a blood disorder or illness that affects your blood cell counts, a full blood will help to monitor your condition.

  • To monitor medical treatment you are having. A full blood count can also be used to monitor your health during any medical treatment including medications you are taking that might affect your blood cell counts.

How should I prepare and what's involved in a full blood count?

You can eat and drink normally, and there is no need to prepare in any way for a full blood count test. However, it may be worth thinking about wearing loose-fitting sleeves or a sleeveless top that can be easily rolled up for the blood to be taken.

The GP or nurse will simply insert a needle into a vein in your arm, usually at the bend in your elbow. They may pop a plaster on afterwards to protect your clothing and allow your blood to clot around the injection site. You can return to normality and do everything you normally would. Your GP will send your blood sample to a lab for medical analysis.

What could go wrong during or after a full blood count?

During a blood test, your GP may have difficulty finding your vein and may ask you to clench and unclench your fist in order to find a flow of blood. 

Errors can sometimes occur, as nothing is really foolproof. It is for this reason that the GP may want to conduct another test. Errors in the test could include failure of the equipment, the incorrect labelling of the sample (we're all human), contamination or incorrect handling or if alcohol is found in the blood. It is for any of these reasons that you might have to have another test conducted.

What are the normal values for a full blood count?

Haemoglobin in adults should be 130-170g/L in men and 115-150g/L in women. White blood count should be 4.0-10.0 x 109/L for adults and the platelet count should be 150-400 x 109/L for adults. These values are a guide and can be influenced by many factors including age and pregnancy. It is for this reason that you ask for a clear diagnosis and explanation from a GP, who will be able to appropriately translate the results for you.

Is there a chance I will need further tests?

If the GP finds an abnormality in your blood, it is likely that you will need further tests to determine the cause. If your blood count comes back as normal, then your onward treatment will depend on your reason for having the test. If you are unwell, the GP may try other tests to determine the cause of your illness.

In summary

In summary, a full or complete blood count is used to evaluate your overall health and detect a range of disorders or infections. There are a number of reasons why a GP may suggest you have this test conducted. Conversely, you may be the one looking to have this test done, to check your overall health or as part of a full health check. Whatever the reason, this test is useful for picking up abnormalities in the blood and can lead to further test and diagnoses. 

Have a full blood count with Vaila Health

At Vaila Health, we offer full blood counts both separately and as part of a comprehensive health check. Your blood will be drawn by a fully-qualified GP who will deal with all of the aspects of your sample and results processing and will get back to you with a clear results diagnosis. 

For a full blood count, you can book in for a standard GP appointment and you will pay just £99 for the consultation and blood test. Book your consultation now

If you would like a bit of a health "MOT", you can book one of our Health Checks here:

Core Health Check £295

Well Woman Health Check £450

Well Man Health Check £450


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