White blood cells count:
A WBC count is a blood test to measure the number of white blood cells
(WBCs).
White blood cells help fight infections. They are also called leukocytes.
There are five major types of white blood cells:
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Neutrophils
Lymphocytes (T cells and B cells)
Monocytes
Eosinophils
Basophils
Total white blood cells - All the white cell types are given as a
percentage and as an absolute number per litre.
Neutrophil granulocytes - May indicate bacterial infection. May also be
raised in acute viral infections.
Neutrophils are phagocytes, capable of ingesting microorganisms or
particles. They can internalize and kill many microbes, each phagocytic
event resulting in the formation of a phagosome into which reactive
oxygen species and hydrolytic enzymes are secreted. The consumption of
oxygen during the generation of reactive oxygen species has been termed
the "respiratory burst," although unrelated to respiration or energy
production.
The respiratory burst involves the activation of the enzyme NADPH
oxidase, which produces large quantities of superoxide, a reactive oxygen
species. Superoxide dismutates, spontaneously or through catalysis via
enzymes known as superoxide dismutases (Cu/ZnSOD and MnSOD), to
hydrogen peroxide, which is then converted to hypochlorous acid HOCl,
by the green heme enzyme myeloperoxidase. It is thought that the
bactericidal properties of HOCl are enough to kill bacteria phagocytosed
by the neutrophil, but this may instead be step necessary for the activation
of proteases.
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Lymphocytes - Higher with some viral infections such as glandular fever
and. Also raised in lymphocytic leukemia. Can be decreased by HIV
infection. In adults, lymphocytes are the second most common WBC type
after neutrophils. In young children under age 8, lymphocytes are more
common than neutrophils.
LYMPHOCYTE FUNCTION OF
CLASS
LYMPHOCYTE
Lysis of virally infected cells and
NK cells
tumour cells
Release cytokines and growth
factors that regulate other immune
Helper T cells
cells
Lysis of virally infected cells,
Cytotoxic T cells
tumour cells and allografts
Immunoregulation and cytotoxicity
γδ T cells
Secretion of antibodies
B cells
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PROPORTION
7% (2-13%)
46% (28-59%)
19% (13-32%)
23% (18-47%)
Monocytes - May be raised in bacterial infection, tuberculosis, malaria,
monocytic leukemia, chronic ulcerative colitis and regional enteritis.
Monocyte is a type of white blood cell, part of the human body's immune
system. Monocytes have two main functions in the immune system: (1)
replenish resident macrophages and dendritic cells under normal states,
and (2) in response to inflammation signals, monocytes can move quickly
(approx. 8-12 hours) to sites of infection in the tissues and
divide/differentiate into macrophages and dendritic cells to elicit an
immune response. Half of them are stored in the spleen. Monocytes are
usually identified in stained smears by their large bilobate nucleus.
Eosinophil granulocytes - Increased in parasitic infections, asthma, or
allergic reaction.
Basophil granulocytes- May be increased in bone marrow related
conditions such as leukemia or lymphoma.
Overview table
Type
Approx
.%
Microscopic in
Diameter
Main targets
Appearance adults (μm)
Blood valu
es
Nucleus
Granules
Lifetime
Neutrophil
54–62% 10–12
Eosinophil
1–6%
10–12
Basophil
<1%
12–15
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Macrophage
bi-lobed
or trilobed
large blue
?
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in allergic reactions
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B cells: various
pathogens
T cells:
o CD4+(helper):
extracellular
bacteria
broken down
into peptides
presented by
MHC class 2 deeply
molecule.
staining,
o CD8+
eccentric
cytotoxic T
cells: virusinfected and
tumor cells.
o γδ T cells:
Natural killer cells:
virus-infected and
tumor cells.
25–33% 7–8
2–8%
8–12 days
(circulate for
4–5 hours)
parasites
in allergic reactions
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Monocyte
bi-lobed
full of
pinkorange
(H&E
Stain)
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Lymphocyte
bacteria
fungi
6 hours–few
fine, faintly days
multilobed pink (H&E (days in
Stain)
spleen and
other tissue)
14–17
Monocytes migrate from the
bloodstream to other tissues
kidney
and differentiate into tissue
shaped
resident macrophages or
dendritic cells.
21
(human)
Phagocytosis (engulfment
and digestion) of cellular
debris and pathogens, and
stimulation of lymphocytes
and other immune cells that
respond to the pathogen.
NK-cells
and
weeks to
Cytotoxic
years
(CD8+) Tcells
hours to
days
none
activated:
days
immature:
months to
years
Main function is as an
antigen-presenting cell
(APC) that activates T
lymphocytes.
Dendritic
cells
The Test is Performed
Blood is typically drawn from a vein, usually from the inside of the
elbow or the back of the hand. The site is cleaned with germ-killing
medicine (antiseptic). The health care provider wraps an elastic band
around the upper arm to apply pressure to the area and make the vein
swell with blood.
Next, the health care provider gently inserts a needle into the vein. The
blood collects into an airtight vial or tube attached to the needle. The
elastic band is removed from your arm.
Once the blood has been collected, the needle is removed, and the
puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to
puncture the skin and make it bleed. The blood collects into a small glass
tube called a pipette, or onto a slide or test strip. A bandage may be
placed over the area if there is any bleeding.
The blood sample is sent to a laboratory. A WBC count is almost always
done as part of a complete blood count (CBC).
Samples
A phlebotomist collects the specimen, in this case blood is drawn in a test
tube containing an anticoagulant (EDTA, sometimes citrate) to stop it
from clotting, and transported to a laboratory.
In the past, counting the cells in a patient's blood was performed
manually, by viewing a slide prepared with a sample of the patient's
blood under a microscope (a blood film, or peripheral smear). Nowadays,
this process is generally automated by use of an automated analyzer, with
only approximately 30% samples now being examined manually.
Manual blood count
similar to
macrophages
Counting chambers that hold a specified volume of diluted blood (as
there are far too many cells if it is not diluted) are used to calculate the
number of red and white cells per litre of blood.
To identify the numbers of different white cells, a blood film is made, and
a large number of white cells (at least 100) are counted. This gives the
percentage of cells that are of each type. By multiplying the percentage
with the total number of white blood cells, the absolute number of each
type of white cell can be obtained.
The advantage of manual counting is that automated analysers are not
reliable at counting abnormal cells.
Normal Results
4,500-10,000 white blood cells per microliter (mcL).
Abnormal Results Mean
A low number of WBCs is called leukopenia. It may be due to:
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Bone marrow failure (for example, due to infection, tumor, or
abnormal scarring)
Collagen-vascular diseases (such as lupus erythematosus)
Disease of the liver or spleen
Radiation therapy or exposure
A high number of WBCs is called leukocytosis. It may be due to:
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Anemia
Infectious diseases
Inflammatory disease (such as rheumatoid arthritis or allergy)
Leukemia
Severe emotional or physical stress
Tissue damage (for example, burns)
Drugs that may increase WBC counts include:
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Aspirin
Chloroform
Corticosteroids
Heparin
Drugs that may lower your WBC count include:
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Antibiotics
Antihistamines
Antithyroid drugs
Chemotherapy drugs
Diuretics
Sulfonamides