Summary

• The Full Blood Count (FBC) is a group of tests that are routinely used to assess someone’s general health or to check for disorders that affect blood cells.
• It counts and measures the different cells in your blood, including red blood cells, white blood cells and platelets.
• Each of these types of blood cells have specific functions and assessing them can give important information.

What is your blood made of?

Your blood is made up of Red Blood Cells (RBCs), White blood Cells (WBCs) and platelets. These float in fluid called plasma.

Blood cells are continually being renewed

To stay healthy, your body must make new blood cells to replace those that age and degrade or are lost through bleeding.

Blood cells are continually being renewed. New cells are produced in the bone marrow, the soft fibrous tissue inside many bones, and then released into your blood stream.

Blood cells develop from stem cells and mature within the bone marrow until they are released into the blood. Red cells live for about 120 days, platelets live for about six days, and the lifespan of white blood cells depend on the type – most last for only a few hours although some last for many years.

The solid part of blood

Red blood cells (RBC)

RBCs are the most common type of blood cell – they make up almost half of your blood - and they play an essential role in carrying oxygen. All cells in every part of your body need oxygen to make energy so that they can function properly.

Red blood cells can carry oxygen because they contain haemoglobin, the red protein that gives RBCs their colour.

If your haemoglobin levels are low, or if you have too few RBCs, your body will not be able to get enough oxygen, causing fatigue and weakness.

White blood cells (WBC)

If you have an infection or inflammation somewhere in your body, your white cell production goes up. WBCs, or leukocytes, are your body’s defence against anything entering your body that can cause harm. They fight infection, help create immunity, and clean up damaged cells. WBCs are released from the bone marrow in higher amounts than normal when an infection is detected by the body. They travel in the blood to the site of infection and when they have completed their task, bone marrow production returns to normal levels.
There are five types of WBCs, all with different functions:

• Neutrophils are the most common type of circulating WBCs. They engulf and destroy harmful microorganisms like bacteria and viruses in damaged or infected tissue.
• Monocytes travel through the blood where they become macrophages. They kill harmful microorganisms and remove dead cells.
• Eosinophils respond to infections caused by parasites, play a role in allergic reactions and control the extent of immune responses.
• Basophils are the least common WBC and are also involved in allergic reactions.
• Lymphocytes can be found in the lymphatic system (which drains excess fluid from the body and blood) and come in three types:
  • B lymphocytes (B cells) produce antibodies that recognise and flag foreign cells for destruction,
  • T lymphocytes (T cells) recognise foreign substances and processes them for removal, and
  • Natural Killer cells (NK cells) directly attack and destroy cancerous cells or cells infected with a virus.

Platelets

Platelets are tiny plate-shaped cells that circulate in your blood. They bind together to form clots when blood vessels are injured. These clots create a temporary plug in broken blood vessels to stop bleeding.

When they become activated, they change their shape by growing long tentacles and stick to each other. Platelets also release chemicals to attract more platelets and other cells, setting off the next step in what is called the coagulation cascade.

The liquid part of blood

Plasma

This is a pale-yellow liquid that represents about half of the content of whole blood. It contains water, salt and proteins that help blood to clot, transport nutrients, minerals and hormones throughout your body.

Why get tested?

The FBC helps to screen, diagnose and monitor a wide range of disorders and conditions such as anaemia, blood clotting problems, infections, blood cancer and immune system disorders.

What does the FBC examine?

Each test in the FBC gives different information. Looked at together, along with your symptoms and medical history, they help build a picture of the health of your blood.

Having the test

Sample
Blood.

Any preparation?
None.

Your results

Reading your test report

Your results will be presented along with any other tests your doctor ordered on the same form. You will see separate columns or lines for each of these tests. Your results may be flagged as high (H) or low (L).

Reference intervals - comparing your results to the healthy population

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• They are used to provide a benchmark for interpreting a patient's test results.
• When compared against them, your results may be flagged high or low if they sit outside this range.
• Some reference intervals are harmonised or standardised, which means all labs in Australia use them.
• Others are not because for these tests, labs are using different instruments and chemical processes to analyse samples.
• Always compare your lab results to the reference interval provided on the same report.
• If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation.

Reference intervals for the various components of the FBC vary slightly between laboratories in Australia because they use different measurement instruments. Always check your specific laboratory’s ranges.

Key components like Hb, RBC, HCT, WBC and platelets have distinct ranges depending on age, gender and factors like pregnancy, altitude and smoking.

Further testing

The FBC is performed on laboratory analysers that automatically count the different components. If some of your results are unclear, the laboratory may go on to perform a blood film in which a scientist or haematologist (pathologist) examines your blood under a microscope. They look more closely at the appearance of the blood cells, such as size, shape and colour, searching for anything unusual.

Any more to know?

There is no way you can directly raise the number of your WBCs or change the size or shape of your RBCs. Addressing any underlying diseases or conditions and following a healthy lifestyle will help optimise your body's cell production and your body will take care of the rest.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements, as these may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More Information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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