Download Whole Blood Count The full blood count (FBC) is one of the most

Whole Blood Count
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).
How is it used?
The FBC is used as a broad screening test to check for such disorders as anaemia, infection, and many other diseases. It
is actually a panel of tests that examines different parts of the blood and includes the following:
 White blood cell (WBC) count is a count of the actual number of white blood cells per volume of blood. Both
increases and decreases can be significant.
 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 (also known as PMNs or neuts), lymphocytes, monocytes,
eosinophils, and basophils.
 Red blood cell (RBC) count: is a count of the actual number of red blood cells per volume of blood. Both
increases and decreases can point to abnormal conditions.
 Haemoglobin measures the amount of oxygen-carrying protein in the blood.
 Haematocrit measures the amount of space red blood cells take up in the blood. It is reported as a percentage (0
to 100) or a proportion (0 to 1).
 The platelet count is the number of platelets in a given volume of blood. Both increases and decreases can point
to bleeding or clotting disorders.
 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.
 Mean corpuscular volume (MCV) is a measurement of the average size of your RBCs. The MCV is elevated when
your RBCs are larger than normal (macrocytic), for example in anaemia caused by vitamin B12 deficiency or folic
acid deficiency. When the MCV is decreased, your RBCs are smaller than normal (microcytic), which may indicate
iron deficiency anaemia, inflammation or occasionally 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, long standing inflammation or
thalassaemia. Increased MCHC values (hyperchromia) are seen in conditions where the haemoglobin is
abnormally concentrated inside the red cells, such as in hereditary or autoimmune spherocytosis.
 Red cell distribution width (RDW) is a calculation of the variation in the size of your RBCs. In some anaemias,
such as iron deficiency or 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?
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 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.
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?
The following table explains what increases or decreases in each of the components of the FBC may mean.
TEST
WBC
NAME
White Blood Cell
INCREASED/DECREASED
May be increased with infections, inflammation, cancer, leukaemia;
May be decreased with some medications, 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)
%
Neutrophil/Band/ANC This is a dynamic population that varies somewhat from day to day depending on
Neutrophil
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
Lymphs
Lymphocyte
% Mono
Monocyte
% Eos
Eosinophil
% Baso
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
Hct
Haematocrit
Mirrors RBC results
MCV
Mean Corpuscular
Volume
Increased with: B12 and Folate deficiency, liver disease, underactive thyroid,
pregnancy, alcohol excess, some bone marrow disorders;
decreased with: iron deficiency, longstanding inflammatory disorders and
thalassaemia
MCH
Mean Corpuscular
Haemoglobin
May be low in iron deficiency, inflammatory conditions and thalassaemia
MCHC
Mean Corpuscular
Haemoglobin
Concentration
Helps with interpretation of MCH
RDW
RBC Distribution
Width
Increased RDW indicates abnormal variation in RBC size. Can indicate iron
deficiency or bone marrow disorders.
Platelet
Platelet
Increased numbers of platelets occur with bleeding, inflammation, bone marrow
disorders and in patients with absent or underactive spleens.
Decreased numbers are associated with immune conditions such as ITP and SLE,
vitamin deficiencies, some drugs (especially chemotherapy), alcoholism, liver
disease, enlarged spleens, bone marrow disorders and with some rare inherited
disorders (such as Wiskott-Aldrich, Bernard-Soulier)
MPV
Mean Platelet Volume Vary with platelet production; younger platelets are larger than older ones
Adapted from: http://www.labtestsonline.org.uk/understanding/analytes/cbc/test.html