FBC
What is a full blood count and why is it done?
A full blood count, (FBC) also known as complete blood count (CBC) often the “starting point” for most medical investigations. An FBC not only tests for disorders and abnormalities of the blood but, as blood travels throughout the whole body, it can give an indication of disease present in various organs.
An FBC is used to obtain a count of the blood cells and it is used to estimate the levels of different blood cells within the body’s blood system in the sample of blood taken. Blood is made up from three main types of blood cell: red blood cells, white blood cells and platelets. The number of cells present, the size and proportions of these cells, and the haemoglobin (oxygen carrying component of red blood cells) are measured in an FBC.
Why would I need this test?
An FBC test may be requested as a routine blood test to find out about your general health. It may also be used to help with diagnosis and monitoring of different conditions and treatments. An FBC can be used to:
Investigate deficiencies such as vitamin B12 or folate deficiency or iron deficiency anaemia
- Help diagnose infection
- Help diagnose blood disorders
- Monitor the response to some types of medication or radiation treatment
- Investigate abnormal bleeding or clotting.
How do I prepare for an FBC test?
There is no preparation necessary for a full blood count. It can be done at any time of the day.
What do the results of my FBC test mean?
Interpreting blood test results is not always easy and is best done in consultation with your healthcare team. Sometimes, however, a full blood count can present abnormal results that are indicative of more serious diseases, each abnormality in concentration of a specific type of blood cell can be indicative of specific problems.
The information below must be used as a guide only. If you have an abnormal blood count, your doctor will determine what treatment is necessary.
Platelets
These are the cell responsible for the clotting of the blood to stop wounds bleeding. The platelets stick together at the site of an open wound to form a temporary barrier from the external area.
Normal
The normal platelet count is 150–400 billion platelets per litre of blood (or 150-400 x 109/L). As you can imagine, this would make cells very small!
Low
A low blood platelet count can be due to a condition called thrombocytopenia. Some drugs can cause a low platelet count. If this is the case, platelet levels will return to normal after stopping the drug. Symptoms can include excessive bleeding or bruising.
High
A high platelet count can be due to a condition called thrombocytosis. This condition can predispose a patient to thrombosis in certain situations. People diagnosed with this should be very wary of situations that require them to remain in the same position for a long time as the blood can get “stuck”. If you work in an office environment, make sure you get up at least once an hour: stretch your legs, take a walk or stroll. Plane rides are another risk for people with thrombocytosis.
Red blood cells (erythrocytes)
The major function of the red blood cell is to transport oxygen to all parts of the body. Red blood cells are made continuously in the bone marrow, and are released into the blood stream to replace the old circulating blood cells. 4.5 million to 5.9 million cells/mcL for men; 4.1 million to 5.1 million cells/mcL for women.
Normal
As haemoglobin is a chemical in a cell rather than a cell itself, it is measured by weight. The normal haemoglobin content of red blood cells is 115–150 grams per litre. This equates to approximately 27–34 picograms per red blood cell in one litre of blood. A picogram is one trillionth of a gram, or 1 x 10-12 grams. The normal volume of red blood cells in one litre of blood is 77-98 femtolitres. A femtolitre is even smaller than a picolitre (1 x 10-15 litres).
Low
Low haemoglobin content is the most common abnormality found in routine FBCs. This is a condition known as anaemia. Anaemia can be present with or without an iron deficiency. Our doctors' will likely assess your diet and history of drug use in order to determine the appropriate treatment.
High
Polycythaemia is associated with an abnormally high haemoglobin concentration in the blood, and is an indication that red blood cell numbers are also too high. This could be due to respiratory or circulatory disorders or, in some cases, to a tumour. Sometimes a high red blood cell count is due to dehydration.
White blood cells (leukocytes)
White blood cells function as part of the body’s immune system. They help to protect the body from infection and disease. There are several different types of white blood cell:
- Neutrophils
- Lymphocytes
- Monocytes
- Eosinophils
Normal
The combined white cell count is normally 4–10 billion cells per litre of blood.
Low
A low neutrophil count can be associated with infection. This condition is named neutropenia. Low white blood cells can also be indicative of a bone marrow disorder.
High
The primary diagnosis for a high white blood cell count is leukocytosis. It is possible that a person with leukocytosis may have lymphoma or leukaemia. Therefore, our doctors will need to assess your history and take further blood tests. If the count returns high again, they will refer you to a specialist. Raised eosinophil counts are most commonly the result of allergies or asthma. If your blood cell counts are abnormal, it is important that you have frequent check-ups to make sure serious problems do not develop.
