At a glance

Also known as

FBC; FBE (full blood examination); FBP (full blood picture); CBC (complete blood count); CBE; CBP

Why get tested?

To determine general health status and to screen for a variety of disorders, such as anaemia and infection, as well as nutritional status and exposure to toxic substances

When to get tested?

As part of a routine medical examination or as determined by your doctor

Sample required?

A blood sample drawn from a vein in the arm or a finger-prick or heel-prick (newborns)

What is being tested?

The full blood count (FBC) is one of the most commonly ordered tests and provides important information about the kinds and numbers of cells in the blood: red blood cells, white blood cells and platelets. Abnormalities in any of these types of cells can indicate the presence of important medical disorders.

Blood is composed of a variety of living cells that circulate through the heart, arteries and veins carrying nourishment, hormones, vitamins, antibodies, heat and oxygen to the body's tissues. Blood contains three main components - red blood cells, white blood cells, and platelets - suspended in fluid, called plasma. Red blood cells contain haemoglobin, a protein that carries oxygen to all the tissues of the body. Among other functions, white blood cells are responsible for protecting the body from invasion by foreign substances such as bacteria, fungi and viruses. White blood cells also control the immune process. Platelets help the blood clotting process by plugging holes in broken blood vessels.

How is the sample collected for testing?

The FBC is performed on a blood sample taken by a needle placed in a vein in the arm or by a finger-prick (for children and adults) or heel-prick (for infants).

The Test

How is it used?

The FBC is used as a broad screening test to check for such disorders as anaemia (decrease in red blood cells or haemoglobin), infection, and many other diseases. It is actually a group of tests that examine different parts of the blood. Results from the following tests provide the broadest picture of your health:

  • White blood cell (WBC) count measures the total number of white blood cells. Both increases and decreases can be significant. A typical WBC in an adult is 4 - 11 x 109/L (four to eleven thousand million per litre of blood).
  • White blood cell differential: looks at the types of white blood cells present. There are five different types of white blood cells, each with its own function in protecting us from infection. The differential classifies a person's white blood cells into each type: neutrophils , lymphocytes, monocytes, eosinophils, and basophils.
  • Red blood cell (RBC) count: the number of red blood cells per litre of blood. Both increases and decreases can point to abnormal conditions. Red blood cells are reported as billions per litre (4.25x1012/L).
  • Haemoglobin: is the iron containing oxygen-carrying protein in the red cells. Haemoglobin values are higher in males than in females and results are reported in units of g/L or g/dL (125 g/L is equivalent to 12.5 g/dL).
  • Haematocrit: the proportion of space red blood cells take up in the blood. It is reported as a ratio.
  • Platelet count: the number of platelets in a given volume of blood. Both increases and decreases can point to abnormal conditions of excess bleeding or clotting. Mean platelet volume (MPV) is a machine-calculated measurement of the average size of your platelets. New platelets are larger, and an increased MPV occurs when increased numbers of platelets are being produced. MPV gives your doctor information about platelet production in your bone marrow. Platelets are reported as thousand millions per litre (150 - 400 x 109/L).
  • Mean corpuscular volume (MCV): a measurement of the average size of your red blood cells (RBC). The MCV is elevated when your RBCs are larger than normal (macrocytic), for example in anaemia caused by vitamin B12 deficiency. When the MCV is decreased, your RBCs are smaller than normal (microcytic), such as is seen in iron deficiency anaemia, or thalassaemias.
  • Mean corpuscular haemoglobin (MCH) is a calculation of the amount of oxygen-carrying haemoglobin inside your RBCs. Since macrocytic RBCs are larger than either normal or microcytic RBCs, they would also tend to have higher MCH values.
  • Mean corpuscular haemoglobin concentration (MCHC) is a calculation of the concentration of haemoglobin inside the RBCs. Decreased MCHC values (hypochromia) are seen in conditions where the haemoglobin is abnormally diluted inside the red cells, such as in iron deficiency anaemia and in thalassaemia. Increased MCHC values (hyperchromia) are seen in conditions where the haemoglobin is abnormally concentrated inside the red cells, such as in hereditary spherocytosis, a relatively rare congenital disorder.
  • Red cell distribution width (RDW) is a calculation of the variation in the size of your RBCs. In some anaemias, such as pernicious anaemia, the amount of variation (anisocytosis) in RBC size (along with variation in shape - poikilocytosis) causes an increase in the RDW.

When is it requested?

An FBC is usually requested as a routine blood test. It is also requested for a variety of other more specific situations. These can include:

  • to determine how severe a blood loss is
  • to help diagnose infection
  • to help diagnose diseases such as leukaemia or anaemia
  • to monitor the response to some types of drug or radiation treatment
  • to investigate a history of abnormal bleeding or clotting

The FBC is a very common test used to screen for, help diagnose, and to monitor a variety of conditions. Many patients will have baseline FBC tests to help determine their general health status. If they are healthy and they have cell populations that are within normal limits, then they may not require another FBC until their health status changes or until their doctor feels that it is necessary.

If a patient is having symptoms associated with anaemia, such as fatigue (tiredness) or weakness, or has an infection, inflammation, bruising, or bleeding, then the doctor may order a FBC to help diagnose the cause. Significant increases in WBCs may help confirm that an infection is present and suggest the need for further testing to identify its cause. Decreases in the number of RBCs (anaemia) can be further evaluated by changes in size or shape of the RBCs to help determine if the cause might be decreased production, increased loss, or increased destruction of RBCs. A platelet count that is low or extremely high may confirm the cause of excessive bleeding or clotting and can be associated with disease of the bone marrow such as leukaemia

Many conditions will result in increases or decreases in the cell populations. Some of these conditions may require treatment, while others will resolve on their own. Some diseases, such as cancer (and chemotherapy treatment), can affect bone marrow production of cells, increasing the production of one cell at the expense of others or decreasing overall cell production. Some medications can decrease WBC counts, and some vitamin and mineral deficiencies can cause anaemia. The FBC test may be ordered by the doctor on a regular basis to monitor these conditions and drug treatments.

What does the test result mean?

Looking for reference ranges?

The following table explains what increases or decreases in each of the components of the FBC may mean.

Components of the FBC

Test Name Increased/decreased
WBC                    White blood cell May be increased with infections, inflammation, cancer, leukaemia; decreased with some medications (such as methotrexate), some autoimmune conditions, some viral or severe infections, bone marrow failure, enlarged spleen, liver disease, alcohol excess and congenital marrow aplasia (marrow doesn't develop normally)
%Neutrophils Neutrophil/PMNs/Neuts This is a dynamic population that varies somewhat from day to day depending on what is going on in the body. Significant increases in particular types are associated with different temporary/acute and/or chronic conditions.  An example of this is the increased number of lymphocytes seen with lymphocytic leukaemia. For more information, see Blood film and WBC.
%Lymphocytes Lymphocyte
%Monocytes Monocyte
%Eosinophils Eosinophil
%Basophils Basophil
RBC Red Blood Cell Decreased with anaemia; increased when too many made and with fluid loss due to diarrhoea, dehydration, burns
Hb Haemoglobin Mirrors RBC results
PCV Haematocrit Mirrors RBC results
MCV Mean corpuscular volume increased with vitaminb B12 and folate deficiency ; decreased with iron deficiency and thalassaemia
MCH Mean corpuscular haemoglobin Mirrors MCV results
MCHC Mean corpuscular haemoglobin concentration May be decreased when MCV is decreased; increases limited to amount of Hb that will fit inside a RBC
RDW RBC distribution width Increased RDW indicates mixed population of RBCs; immature RBCs tend to be larger
Platelet Platelet Decreased or increased with conditions that affect platelet production; decreased when greater numbers used, as with bleeding; decreased with some inherited disorders (such as Wiskott-Aldrich, Bernard-Soulier), with Systemic lupus erythematosus, pernicious anaemia, hypersplenism (spleen takes too many out of circulation), leukaemia, and chemotherapy
MPV Mean platelet volume Vary with platelet production; younger platelets are larger than older ones

Common Questions

What can a patient do about his FBC?

Patients who have a keen interest in their own health care frequently want to know what they can do to change their WBCs, RBCs, and platelets. Unlike 'good' and 'bad' cholesterol, cell populations are not generally affected by lifestyle changes unless the patient has an underlying deficiency (such as vitamin B12 or folate deficiency or iron deficiency). There is no way that a patient can directly raise the number of their WBCs or change the size or shape of their 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.

Last Review Date: November 29, 2012