The capillaries act as an exchange system that connects the smallest veins with the smallest arteries.
Veins carry blood to the heart whereas arteries carry blood away from the heart and to the tissues.
WHERE ARE WHITE BLOOD CELLS MADE?
White blood cells are created by a type of cell in the bone marrow (a type of tissue inside of the bones)
known as hematopoietic stem cells (HSCs), which are cells that give rise to other cells. HSCs are also
known as hemocytoblasts, hemoblasts, and lymphoidocytes. Some lymphocytes mature in organs that
are part of the lymphatic system such as lymph nodes, the spleen, or thymus gland. Lymph nodes are
small egg shaped structures in the body that help fight against infection. The spleen is an organ next to
the stomach that helps fight infection and removes and destroys worn-out red blood cells. The thymus
gland is an organ located in the upper part of the chest and is very important in producing substances
that protect the body against disease.
HOW LONG DO WHITE BLOOD CELLS LIVE FOR?
Mature white blood cells typically live for a few hours to 3 to 4 days in the average person. However,
some white blood cells can live for a few weeks. Life expectancy of white blood cells varies according to
type, which is discussed in more detail below. The survival of white blood cells depends on their
continuous production of energy. The chemical paths used by white blood cells are more complex than
red blood cells and similar to other tissue cells. They do not undergo cell division (known as mitosis) in
the blood although some have the capability of cell division.
WHAT ARE THE DIFFERENT TYPES OF WHITE BLOOD CELLS?
There are five main types of white blood cells, which can be quantified on the complete blood count test
with differential. Differential means that instead of only providing the total white blood cell count that the
different types (aka differential) of white blood cells are listed. The white blood cell count is almost
always part of the complete blood count (CBC) test, which provides important information about the
kinds and numbers of cells in the blood.
The different types of white blood cells each have many shared features but are each differ in structure
and function, such as fighting against different types of diseases. They are categorized in two groups
(granulocytes and agranulocytes) depending on their cytoplasm contents. Cytoplasm is a gel-like
substance found inside the membrane (outer surface) of a cell.
The different types of white blood cells are listed below. Click to learn more about each one.
GRANULOCYTES (aka polymorphonuclear leukocytes): These types of white blood cells have
granules (tiny substances that release specialized chemicals) that stain differently in their cytoplasm
when viewed under a high powered microscope. The granules in granulocytes are usually lysozymes
(enzymes that damage the cell wall of bacteria) and work by digesting engulfed cell particles. An enzyme
is a type of protein that helps produce chemical reactions in the body. When a granulocyte is released in
the blood, it stays there for about four to twelve hours and then travels to the tissues of the body, where
it remains for four to eight days. However, these times may be shorter in cases of severe infection.
The three types of granulocytes are listed below, which are named according to how they absorb dyes in
Basophils: Basophils help protect the body against disease and infections by eating some types of
bacteria, foreign substances, and other cells. They make up about 1% to less than 1% of white blood
cells. Basophils are the smallest of the granulocytes. They also release a chemical called histamine
which provides an inflammatory response in the body. They also release a chemical called heparin,
which promotes blood flow to damaged areas and provides defense at such sites against bacteria and
other foreign materials.
Eosinophils: Eosinophils help protect the body against disease and infections by moving around and
eating some types of bacteria, foreign substances, and other cells. They make up about 2 to 3% of
white blood cells. They are very helpful in defending the body against parasites. A parasite is any
organism that lives in or on another living being, gains an advantage by doing so, but causes
disadvantage to the being it is living on. Eosinophils also help regulate inflammatory responses due to
Neutrophils: Neutrophils are a type of mature (developed) white blood cell that is present in the blood
which mainly targets bacteria and viruses. They make up about 54 to 62%% of white blood cells and are
the first to arrive at an infection site to ingest invasive organisms. Immature neutrophils in the blood
(known as bands) make up about 3% of white blood cells.
AGRANULOCYTES (mononuclear leukocytes): These types of white blood cells are named because
they appear to have a lack of granules in the cytoplasm. However, despite their name, they actually do
contain granules that are not readily stained with blue but which break down waste material and cellular
debris. The two types of granulocytes are listed below.
Lymphocytes: Lymphocytes are small white blood cells that help provide a specific response to attack
the invading organisms and tumor cells. There are two types of lymphocytes: T cells and B cells, which
each play different roles in defending the body against what are interpreted as foreign invaders.
Lymphocytes make up about 20 to 40% of white blood cells.
Monocytes: Monocytes are relatively large types of white blood cell with one nucleus (the cell’s control
center). They develop into macrophages that eat bacteria and debris in tissues. At times, they function
as a scavenger type of cell. Along with neutrophils, macrophages are the main white blood cells that
engulf foreign substances in the body to destroy them. Macrophages are much larger and live longer
than neutrophils. Monocytes make up about 2 to 8% of white blood cells. They travel in the blood for
about a day before leaving.
WHY IS IT IMPORTANT TO KNOW THE NUMBER OF WHITE BLOOD CELLS IN THE BODY?
It is important to know how many white blood cells are in the blood because this is an important indicator
of disease. Normal white blood cell counts vary between different laboratories but generally range from
between 4300 and 11,800 per microliter of blood (one millionth of a liter). White blood cells make up
about 1% of the total blood volume in a healthy adult. A drop of blood can contained between 7,000 and
25,000 white blood cells. It is normal for the white blood cell count to change during the day, with low
values during periods of rest and higher values during exercise. Newborns have high levels of white
blood cells that fall to adult levels during childhood. However, the lymphocyte count is different because
it is low at birth, reaches its peak in the first four years of life, and then gradually falls to the adult range
WHAT CAN CAUSE THE WHITE BLOOD CELL COUNT TO BE TOO LOW?
When there are too few white blood cells in the body (typically lower than 4,000 per microliter of blood)
this is known as leukopenia. However, some healthy people have lower white blood cells than what is
considered normal. In children, determining if the white blood cell count is low depends on age and
gender. When a low white blood cell count is found, it is typically expected because the blood test has
been ordered in response to signs and symptoms. Along with other tests, a low white blood cell count
can help identify the cause of an illness. Patients with chronic leukopenia are vulnerable to infections,
which is why it is important to take steps to prevent this such as hand washing, avoiding sick contacts
with others, and thorough hand washing.
Deficiency or failure of bone marrow can also cause low white blood cells. This can be caused by
infection, abnormal scarring, or tumor(s). For example, some viral infections can cause a low white blood
cell count because the virus temporarily disrupts bone marrow function (where white blood cells are
made). Some infections can be so significant that they use up white blood cells faster than they can be
produced, resulting in a low blood cell count. There are some conditions that children are born with that
are characterized by decreased bone marrow function. Cancer of the bone marrow can cause
leukopenia. Cancer is an abnormal growth of new tissue characterized by the uncontrolled growth of
abnormally structured cells that have a more primitive form. Leukopenia can be caused by exposure to
radiation (such as when it is used to treat cancer).
Anaplastic anemia can cause low white blood cells. Anaplastic anemia is a condition in which the body
stops producing enough blood cells due to bone marrow damage. Myelodysplastic syndrome is a broad
term for diverse conditions that damage the hematopoietic stem cells in bone marrow that make white
blood cells. As a result, this can cause a low white blood cell count. White blood cells are pictured to the
right under the microscope.
Another cause of low white blood cells is collagen-vascular diseases, which are diseases in which the
body reacts against its own tissue. An example is systemic lupus erythematosus (SLE). SLE is a long-
term disease in which the connective tissues throughout the body are inflamed because the body's
defense system attacks these tissues as if they were foreign substances. Conditions where the body’s
immune system attacks itself are known as autoimmune disorders. When an autoimmune disorder
destroys white blood cells or bone marrow, the white blood cell count can be low.
HIV (human immunodeficiency virus) and AIDS (acquired immune deficiency syndrome) can cause a low
white blood cell count. AIDS is a decrease in the effectiveness of the body's immune (defense) system
that is due to infection from HIV (a type of virus). A condition known as Kostmann’s syndrome can cause
leukopenia because it is condition inherited from birth characterized by a severe deficit in neutrophil
production. Another condition inherited from birth that causes a white blood cell reduction is
myelokathexis, which results in a failure of neutrophils to enter the blood.
Diseases of the liver or spleen can also cause low white blood cell counts. The spleen is an organ near
the stomach that helps fight infection and removes and destroys worn-out red blood cells (cells that help
carry oxygen in the blood). An example is hypersplenism (overactive spleen) in which the spleen can
prematurely destroy blood cells. Poor nutrition, a gradual wasting away of mind and body, severe and
potentially deadly allergic reactions (known as anaphylaxis), and vitamin deficiencies are another cause
of low white blood cells. Diseases causes by parasites can also cause a low white blood cell count. A
parasite is an organism that lives in or on another organism to obtain nourishment.
Low white blood cell counts can be caused by medications, which can damage bone marrow, destroy
white blood cells, and affect the functioning of white blood cells. Antibiotics can cause the white blood
cell level to decrease. Other examples of medications that can lower the white blood cell counts
Anticonvulsants: Medications used to treat seizures. A seizure is an overexcitable state of nerve cells in
the brain, sometimes leading to sudden, violent, involuntary contractions of a group of muscles and/or
manifestations of decreased awareness of environmental surroundings (e.g., blank stare with repetitive
Antihistamines: Substances that block the effects of histamine and are often used to treat allergies.
Histamine is a natural substance in the body that is released during allergic reactions and leads to many
Barbiturates: Relaxing drugs that act by depressing breathing rate, blood pressure, and brain
Chemotherapy: Types of medications used to treat cancer.
Clozapine (Clozaril): An anti-psychotic medication. Psychosis is a mental disorder characterize by an
impaired ability to understand reality. With
Clozaril, one of the rare side effects is agranulocytosis, which is the total absence of granulocytes
(basophils, eosinophils, and neutrophils).
Diuretics: Medications that help release water from the body.
Immunosuppressants: Medications that suppress or affect the body’s immune system. This includes
medication to suppress the immune system during organ transplants such as CellCept (mycophenolate
mofetil), Ciclosporin, Prograf (tacrolimus), and Rapamune (sirolimus). Another example are some
medications (known as interferon therapy) used to treat multiple sclerosis such as Avonex and Rebif
(both also known as interferon beta-1a) and Betaseron and Extavia (both known as interferon beta-1b).
Thionamides (anti-thyroid drugs): Drugs used to treat an over-active thyroid gland. The thyroid gland is
a butterfly-shaped organ located in front of the neck that produces a natural chemical known as
hormones that affect virtually every cell in the body and many functions such as disease fighting, heart
rate, energy level, and skin condition.
In addition to medications, arsenic is known to cause a low white blood cell count. Arsenic is a type of
element found inside the earth's crust, which has been used for centuries as a poison because it is
slowly released from the body.
WHAT CAN CAUSE THE WHITE BLOOD CELL COUNT TO BE TOO HIGH?
When there are too many white blood cells in the body (typically more than 11,000 per microliter of
blood), this is known as leukocytosis. However, some healthy people have higher white blood cells than
what is considered normal. In children, determining if the white blood cell count is high depends of age
and gender. When a high white blood cell count is found, it is typically expected because the blood test
has been ordered in response to signs and symptoms. Along with other tests, a high white blood cell
count can help identify the cause of an illness.
People can quickly produce more white blood cells due to infection (viral or bacterial, especially if the
invading organism fights back and persists), tissue damage (e.g., burns), smoking, pain,
pregnancy/labor, intoxications, convulsions, or severe emotional or physical stress. Allergies
(especially severe ones) and other inflammatory conditions can cause a high white blood cell count.
This includes rheumatoid arthritis. Rheumatoid arthritis is another example of an immune disorder in
which the body's defense system attacks its own tissues, causing inflammation of bone joints. Other
immune system disorders can also cause a high white blood cell count.
Another reason for a high white blood cell count is anemia. Anemia is a condition in which there is an
abnormally low amount of hemoglobin in the blood. Hemoglobin is substance present in red blood cells
that helps carry oxygen to cells in the body. High levels of white blood cells can be caused by tumors or
diseases of the bone marrow. An example is myelofibrosis, which can increase the white blood cell
count, in which in which the normal bone marrow is replaced by fibrous tissue (the connective tissue of
Leukemia (e.g., acute or chronic lymphocytic leukemia, acute or chronic myelogenous leukemia) can
cause high white blood cells, as high as 50,000 in one drop of blood. Leukemia is a type of cancer in
the blood in which bone marrow is replaced by early forms of white blood cells.
Other conditions that can cause a high white blood cell count are tuberculosis, whooping cough, and
polycythemia vera. Tuberculosis is a highly infectious diseases characterized by the formation of small
swellings called nodules (or tubercles) in tissues, especially the lungs. Whooping cough is a type of
infection that causes a cough and a whooping sound when breathing in. Polycythemia vera is a
condition of unknown cause in which there is a long-term increase in red blood cells and other types of
There are many medications that can cause the white blood cell count to be too high by increasing their
production. The most common example is aspirin. Another example is chloroform, a toxic chemical
known to cause people to pass out. Another example is epinephrine (commonly known as adrenaline). A
blood thinner known as heparin can cause a white blood cell elevation. Other examples of medications
that can cause a high white blood cell count are:
Corticosteroids: Medications that help reduce inflammation and influence the body’s immune system
Dyrenium (Traimterne): A medication that treats high blood pressure and helps release water from the
Qualaquin (quinine): A medication used to treat malaria, a serious disease caused by parasites that is
spread by mosquitoes.
Zyloprim (allopurinol): Used to treat kidney stones and gout (a type of arthritis).
WHAT IS CELL POPULATION DATA WITH REGARDS TO WHITE BLOOD CELLS?
Cell population data is a way to report on the physical characteristics of white blood cells, including the
volume, presence of immature cells, the presence of malignant (abnormal and harmful) white blood cells,
the presence of granules (known as granularity), and degree of electrical resistance (known as
ARE WHITE BLOOD CELLS BIGGER THAN RED BLOOD CELLS?
Yes, but there are fewer white blood cells than red blood cells in the body.
WHY ARE THEY CALLED WHITE BLOOD CELLS OR LEUKOCYTES?
White blood cells are so named because after they are spun around in a test tube of a blood sample
during laboratory testing, the white blood cells are located in a typically thin white area (known as the
buffy coat) between the red blood cells on the bottom and the plasma on top. Plasma is the fluid
component of the circulating blood that is watery and straw-colored. The buffy coat can sometimes be
green if there are large amounts of neutrophils in the sample. This is because of an enzyme that
neutrophils produce called myeloperoxidase that produces heme. Heme is the iron component of
hemoglobin. The word leukocyte comes from the Greek word “leuko” meaning “white” and the Greek
word "kytos" meaning "cell." Put the two words together and you have "white cell."