What is a full blood count, how is the test done & what does it show?

What is a full blood count?

A full blood count (FBC) is a blood test which is an extremely common investigation. It measures a wide variety of types of cells in the blood which perform different functions abnormalities that may indicate the presence of certain medical disorders. It can help give an indication of general health and give important clues about underlying health problems.

Blood explained

Blood is composed of a variety of living cells that are sited in plasma, and circulate throughout the body. These cells carry out numerous important functions such as supplying oxygen to the body’s tissues, fighting infections and healing injuries.

There are three main types of blood cell:

  • Red blood cells (also known as erythrocytes) contain haemoglobin, which transports oxygen to your organs.
  • White blood cells (also known as leukocytes) are part of your immune system, and help your body to fight infection and inflammation. Different types of white blood cells include lymphocytes, monocytes, eosinophils, neutrophils and basophils.
  • Platelets (also known as thrombocytes) are small cells which help your blood to clot and  stop bleeding. These cells are made in your bone marrow along with red and white blood cells.

How is a full blood count sample taken?

In order to perform a full blood count, a small sample of blood needs to be drawn from the person’s inner arm with a needle. This is commonly undertaken by a nurse or phlebotomist, and the process is quick and usually only produces mild discomfort for a short time. The full procedure normally follows the following steps:

  • The person tested will be asked to sit or lie down.
  • A tourniquet is tightened around the arm to increase blood volume in the veins.
  • The injection site is wiped with an alcohol solution to clean the area and avoid any infection risks.
  • A needle is inserted to draw blood, which is taken from the vein and collected inside a syringe or vial.
  • The tourniquet is removed
  • The needle is removed, and cotton wool will be pressed against the injection site to minimise bleeding.
  • An adhesive dressing is applied to finish the procedure. Minor bruising may occur in the next day or two.

A blood sample can also be taken with a simple finger prick, which is generally an option taken by those who would prefer to take their own sample from the comfort of their own home. Heel-pricks are also used by professionals to test infants.

No test preparation is needed for a full blood count, meaning no fasting is required. This is unless the sample taken is used for additional tests.

Why get a full blood count?

A routine full blood count can be useful even when symptoms aren’t present, as certain illnesses do not present any symptoms until they reach a more advanced stage. Therefore, full blood counts can aid in the early diagnosis and treatment of many diseases, which generally means a higher chance of treatment effectiveness.

A full blood count can also assist doctors in making a diagnosis, as well as monitor the evolution of certain health conditions.

What is tested with a full blood count?

A full blood count consists of a panel of tests which examine various different parts of the blood, including the following:

Red Blood Cells

  • Haemoglobin (Hb): Haemoglobin is a protein which helps transport oxygen to your organs through your bloodstream. It is what gives red blood cells their colour.
  • Mean Cell Volume (MCV): Mean Cell Volume (MCV) is a measure of the average volume of a single red blood cell. If the RBC are smaller than normal this may indicate conditions such as iron deficiency anaemia. If they are larger than normal this may indicate conditions such as anaemia from vitamin b12 or folic acid deficiency, liver disease or an underactive thyroid.
  • Mean Cell Haemoglobin (MCH): Mean Cell Haemoglobin (MCH) is the average amount of haemoglobin in one of your red blood cells. Like MCV, MCH results are sometimes abnormal in case of vitamin or iron deficiency.
  • Mean Cell Haemoglobin Concentration (MCHC): Mean Cell Haemoglobin Concentration (MCHC) is a measure of the average concentration (%) of haemoglobin within a single red blood cell. It can be helpful in determining the cause of any anaemia if the haemoglobin is low.
  • Red Blood Cells (RBC): Your red blood cell count (RBC), also known as an erythrocyte count, measures how many red blood cells you have. Red blood cells contain haemoglobin, which carries oxygen to your body’s tissues.
  • Haematocrit (HTC): Haematocrit (HTC) is a measure of the proportion of your blood which is made up of red blood cells. The Haematocrit reading rises when the number of red blood cells increases or when the blood volume is reduced, for example if you are dehydrated. The reading can decrease when the body decreases its production of red blood cells, which can indicate anaemia.

White blood cells (immunity)

  • White Blood Cells: White blood cells, also known as leukocytes, are cells which help your body to fight infection and inflammation.  As part of your full blood count, you will receive a breakdown of the following types of white blood cells in your bloodstream:
  • Neutrophils: Neutrophils are the most abundant type of white blood cell in your blood. They primarily help to defend your body against bacterial infections.
  • Lymphocytes: Lymphocytes are cells which help to make antibodies and destroy cancer cells.
  • Monocytes: Monocytes are a type of cell which develop into two different types. Dendritic cells help to identify antigens; Macrophages are involved in your body’s immune response.
  • Eosinophils: Eosinophils help to fight infections and boost inflammation. Higher than normal levels are found in parasitic infections, allergic reactions and in some cancers.
  • Basophils: Basophils are the least common type of white blood cells and are released during allergic reactions.


  • Platelets: Platelets are cells in your blood which help your blood to clot. These cells are made in our bone marrow along with red and white blood cells, and are also known as thrombocytes.

What are the normal ranges of a full blood count?

The normal values for a full blood count vary between laboratories and between populations but typical ranges for adults are shown below:

Red blood cell count Male: 4.5-6.5 trillion cells/L*

Female: 3.8-5.8 trillion cells/L

Haemoglobin Male: 130-180 g/L Female: 115-165 g/L
Haematocrit Male: 0.40-0.54 L/L

Female: 0.37-0.47 L/L percent

White blood cell count 3.50-11.0 billion cells/L
Platelet count 150-450 billion/L

* L = liter

What do my full blood count results mean?

Full blood count results that fall outside of the reference ranges may indicate the presence of underlying health problems.

Cell Count Blood count below average Blood count above average
Red blood cell count A result below average could be a sign of anaemia, which causes fatigue and weakness. Anaemia may be caused by blood loss, low levels of iron, folic acid or vitamin B12. It may also pinpoint an underlying medical condition such as kidney or liver disease. A high red blood cell count, also called erythrocytosis, may indicate an underlying medical condition such as polycythaemia vera, chronic lung disease or heart disease. It may also be caused by smoking.
White blood cell count A white blood cell count below average, also called leukopenia, may be caused by viral infections or an underlying health condition such as bone marrow problems, autoimmune disorders, or cancer. Certain medications can also cause a drop in white blood cell. A high white blood cell count may be caused by an infection or inflammation, or simply be caused by a reaction to certain medications. It may be a sign of bone marrow disease, immune system disorders, thyroid problems, or rheumatoid arthritis.
Platelet count A low platelet count, also called thrombocytopenia, may be a side effect from certain medications. However, it can also indicate an underlying health condition such as autoimmune disorders liver disease or viral infections. A high platelet count, also called thrombocytosis, may be a side effect from certain medications. However it can also indicate an underlying health problem such as an inflammatory condition, infections or certain cancers.

What can I do after my full blood count results?

You should talk to your GP if any results fall outside of the normal range. You may need additional tests to rule out certain health conditions and identify the reason for high or low results. Depending on the findings, your GP will be able to recommend treatment accordingly.

It may be that some of the abnormal results can simply be rectified with lifestyle changes. This is the case when the problem detected was a lack of iron, folate or vitamin B12 in your diet. These can be counteracted with dietary changes and possibly supplements. It is essential to note that following a healthy lifestyle helps optimise your body’s cell production, and reduce the chance of diseases developing.

Full blood counts can be undertaken regularly to monitor your general health and help uncover hidden diseases early. Therefore you can keep track of your health and put your mind at ease by having yearly full blood counts.

What are the limitations of a full blood count?

A full blood count isn’t a definitive diagnostic test, and is considered more of a starting point in detecting underlying health issues. Your GP may need to undertake additional tests where required, or decide that follow-up is in fact not needed. In fact, if your results are only slightly above or below the recommended ranges and you are otherwise healthy, it may be that no further action is required. On the other hand, if your results are significantly above or below the recommended ranges, your GP may need to refer you to a specialist.

How can I get a full blood count?

At Bluecrest, we offer a range of packages that include full blood counts, so you can easily assess your blood health and act accordingly.

At Home

You can get a full blood count from the comfort of your own home with our Extra Home Test Kit or our Total Home Test Kit – which also includes a variety of other key readings pertaining to your general health. All you need to do is order your kit, take your own sample, send it back in our pre-addressed return envelope, and wait to receive your results online within 8 days.

At a clinic

Alternatively, you can book a health check with one of our Certified Healthcare professionals at one of over 2,000 mobile clinics nationwide. Our Core and Complete health MOT packages both include a full blood count, in addition to a wide array of health markers for a detailed view of your health.