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What is Complete Blood Count (CBC) ?
Complete Blood Count is a test that
measures the number of cells in the blood. It is a very common
blood test that evaluates the three major types of cells in
blood: red blood cells (RBC), white blood cells (WBC), and
platelets. Abnormally high or low counts of the cells may
indicate the presence of a disease. A CBC is also known as a hemogram.
Blood is a circulating tissue consisting of plasma and cells.
Plasma is the liquid component of the blood in which the cells
are suspended. The blood cells - the RBCs, WBCs, and platelets -
are produced in the bone marrow and released into the
bloodstream as needed.
CBC is a panel of tests that
examines different parts of the blood including
White Blood Cells (WBCs) these cells help defend the body
against infections and foreign substances. There are five basic
types of WBCs - neutrophils, lymphocytes, basophils, eosinophils,
and monocytes. The CBC test finds out whether the WBCs are
present in sufficient numbers to fight infection.
Red Blood Cells (RBCs) - RBCs transport oxygen throughout the
body. The CBC test determines the actual count of the number of
red blood cells per volume of blood.
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Platelets
- Platelets are not complete cells - they are fragments of
cytoplasm from a cell found in the bone marrow called
megakaryocyte. Platelets play a important role in blood
clotting. The purpose of clotting is to stop bleeding. Platelets
cluster together to plug small holes in damaged blood vessels. A
low count of platelets will result in excessive bleeding and
bruising. A high number of platelets will mean thickening and
clotting of blood. The CBC measures the number and size of
platelets present.
Hemoglobin (Hb) - Hemoglobin is the protein molecule within red
blood cells that carries oxygen and gives blood its red color.
The test measures the amount of hemoglobin in a volume of blood.
Hematocrit - Hematocrit is the percentage of whole blood that is
composed of red blood cells.
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Reasons for the test
A complete blood count may be done to
Diagnose the cause of certain symptoms such as fatigue,
weakness, fever, bruising, or weight loss.
Diagnose anemia or reasons for abnormal bleeding.
Diagnose polycythemia vera (stem cell disorder).
Diagnose an infection and other diseases of the blood like
leukemia.
Monitor the response to some types of drug or radiation
treatment.
Check for abnormal values before surgery.
A complete blood count is usually done as part of a routine
physical examination to determine the general state of your
health.
Sample Collection - The test is performed on a blood sample that is taken from a
patient. The blood sample is taken by piercing a vein on the arm
(usually below the elbow) or fingertip using a sharp needle. In
case of infants, the blood will be drawn from the heel. The
blood is collected in small bottles that are attached to the
needles. There is no special preparation needed for having this
test. You usually feel a brief sting or nothing at all as the
needle goes through the skin. The amount of pain you feel
depends on the skill of your health professional drawing the
blood, the condition of your veins, and your sensitivity to
pain.
Risks
There is very little risk of complications from having blood
drawn from a vein:
A small bruise at the puncture site - You can avoid this by
applying pressure on the needle prick site for several minutes
after the needle is withdrawn.
Inflammation of the vein - This condition is called phlebitis
and is usually treated with a warm compress applied several
times daily.
Results
A standard range is not available for this test. Normal values
can vary from lab to lab and depend on age, sex, elevation above
sea level, and type of blood sample.
High values could indicate the
following
High RBC Count
congenital heart disease
cor pulmonale (swelling in the right lower part of the heart)
dehydration
kidney disease
low oxygen tension in the blood
pulmonary fibrosis (hardening of the lung tissue)
liver disease
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High WBC Count
emotional or physical stress
infections
inflammatory diseases
leukemia
tissue damage
lupus
tuberculosis (TB)
rheumatoid arthritis
malnutrition
diseases such as cancer
High Platelet Count
polycythemia vera
post-splenectomy syndrome
primary thrombocytosis
certain malignancies
cancer of the bone marrow
anemia |
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High hematocrit
burns
dehydration
diarrhea
eclampsia (pregnancy complication)
erythrocytosis (abnormal increase in RBCs)
polycythemia vera,
shock
Low values could indicate the following
Low RBC Count
anemia
bone marrow failure
erythropoietin deficiency
hemorrhage (loss of blood)
leukemia
malnutrition
multiple myeloma (cancer of the bone marrow)
overhydration (absorption of too much fluid)
Low WBC Count
bone marrow failure
collagen-vascular diseases
exposure to radiation
liver or spleen disease
chemotherapy
aplastic anemia
viral infections
malaria
alcoholism
AIDS,
lupus
Low Platelet Count
cancer chemotherapy
disseminated intravascular coagulation (DIC)
anemia
idiopathic thrombocytopenic purpura (bleeding disorder)
leukemia
prosthetic heart valve
massive blood transfusion
Low hematocrit
anemia
blood loss
bone marrow failure
leukemia
malnutrition
multiple myeloma
overhydration
rheumatoid arthritis
nutritional deficiency
Factors that can affect the test
The following factors can interfere with the results of your test:
Prolonged use of a tourniquet while drawing the blood sample
Medications can cause low platelet levels. These include steroids,
some antibiotics, diuretics, chemotherapy medications, quinidine,
and meprobamate.
Pregnancy normally causes a low RBC value and an increase in WBCs.
Clumping of platelets in the test tube.
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Article Contributed By: Jaya Suresh
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