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What is a blood
test? Blood tests help a
physician to diagnose and manage a disease. In addition to examining blood
cells, there are many chemicals in the blood that give important
information about the functioning of bodily systems. Important chemicals
that may be measured include cholesterol, thyroid hormone, potassium, and
numerous others. These various chemicals are dissolved in the plasma and
circulate in the blood. For a chemical blood test, blood is drawn from a
patient’s vein and placed in an empty tube and usually allowed to clot;
the fluid portion of the blood after clotting, called serum, is then used
for the various chemical analyses. The
size and number of the tubes of blood used depend on the number of tests
that are needed and the amount of blood needed for each test. The stoppers
on the tubes are color-coded to indicate if an anticoagulant is in the
tube or not, and which anticoagulant is being used. Before the stopper is
put in place, the tubes are evacuated of air. Consequently, they will fill
by inserting the needle of the syringe through the rubber stopper. Blood
is drawn into the tube. What is a blood cell
count? Counting and examining
blood cells are very important in the diagnosis of blood cell diseases. If
the physician wishes to know about the blood cells, the blood must be
collected in a tube that has an anticoagulant in it to prevent blood
clotting. By so doing, the cells are preserved suspended in plasma and can
be stored for several hours without impairing the accuracy of the results.
To
do a blood count, a sample of blood usually is taken from a vein in the
crease of the forearm, placed in a tube containing an anticoagulant and
transported to a hematology laboratory. In the laboratory, a sample of the
blood is put in a machine that can count red and white cells and platelets
and measure the blood hemoglobin. Also, a small drop of blood is spread
into a thin film on a glass slide, dried, and dyes are applied. The dyes
color the different types of blood cells so that they are readily
distinguishable from one another. The slide is examined under a
microscope, the different types of white cells counted, and the cells
examined to see if they are normal or, if abnormal, what the nature of the
changes are. Blood
has several different types of cells in it:
If
all three of the blood cells types are examined, the test is referred to
as a complete blood count or CBC. Some refer to the results as a hemogram.
Why does my
physician request blood cell counts? There
are several reasons why a physician may request blood cell counts. In a
periodic health examination, blood counts, like other features of the
examination, should be normal. Blood cell counts are a sensitive barometer
of many illnesses; their measurement is an important part of a standard
periodic health examination. The
blood cells may be altered as a result of a blood cell disease, or the
counts may be altered as a reaction to another illness. For example, the
white cell count may be elevated if a bacterial infection is present. The
red cell count may be decreased as a result of a specific vitamin
deficiency. The measurement of blood cells can contribute to the diagnosis
of many disorders. If you have a blood
cell disorder, measurement of the blood cell counts is an important index
of the response of the disease to treatment. These counts are also
important to learn the effects of drug treatment or radiation therapy. A
blood count helps the physician to determine if a drug is working or not,
whether the amount of drug a patient is receiving should be adjusted, or
if another drug is needed. What is a normal
blood count? Normal
blood counts fall within the range that has been established by testing
healthy men and women of all ages. The cell counts are compared to those
of healthy individuals of similar age and sex. If a cell count is higher
or lower than normal, the physician will try to determine the explanation
for the abnormal results. The approximate normal ranges of blood cell counts for healthy adults are as follows:
The five types of
normal white cells that are counted are neutrophils, lymphocytes,
monocytes, eosinophils, and basophils. Blood contains about 60%
neutrophils, 30% lymphocytes, 5% monocytes, 4% eosinophils and <1%
basophils. How does leukemia,
lymphoma, and myeloma affect the blood count? White blood cells are
also called leukocytes. Leukemia is the term used for certain diseases
that affect the white blood cells or leukocytes. The different types of
leukemia affect the blood count differently. Persons with acute leukemia
may have a low, a normal, or a high white blood cell count. The white cell
count may occasionally be many times higher than the normal average count
of about 7,000 white cells per microliter of blood. In addition, the
leukemic white blood cells in patients with acute leukemia do not function
normally. Patients with chronic leukemia always have an increase in white
blood cells. Patients
with lymphoma often disturbances in their blood cell counts as the
lymphoma may suppress red blood cell production or because the lymphoma
has spread to the marrow and suppresses all blood cell types. The lymphoma
cells may enter the blood and produce high white blood cell counts made up
of lymphoma cells (abnormal lymphocytes). Patients
with myeloma usually have anemia because the myeloma cells in the marrow
interfere with red blood cell production. Later, all blood cell types may
be decreased by the effects of the myeloma cells in the marrow.
Will treatment
affect my blood count? Chemotherapy and
radiation therapy often affect a person’s blood counts. To measure the
effects, a complete blood count is usually done at appropriate intervals
during therapy to monitor its effects. The effect depends on the drug
used, the dose used, and the duration of the therapy. Red blood cells,
white blood cells, and platelets originate in the bone marrow. If the type
of therapy you are receiving can suppress blood cell production in the
marrow, the red blood cell, white blood count, and platelet count can
decrease. By following your blood counts, your doctor can determine how
the therapy is affecting your body and whether to continue therapy at the
same dose or change the dose or timing of treatment. If the blood counts
do not recover sufficiently between treatments, a transfusion may be
necessary. Should patients keep
track of their blood counts? Some patients want to
know the results of their blood counts and follow the changes that occur.
If anemia develops, it may explain changes in your energy levels or an
inability to carry out tasks that were easy to do before the anemia. If
the white blood cell count drops to very low levels and fever develops, it
is important to contact the physician promptly. If the platelet count is
very low, you may bleed or bruise more easily; and it may be advisable to
minimize activities that involve physical contact or the risk of injury.
These matters should be discussed with your physician. More information on
blood tests: To get more information, talk to your physician or call the Leukemia & Lymphoma Society, 1-800-955-4572. Web sites that discuss blood tests include:
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