$Unique_ID{PAR00009}
$Pretitle{}
$Title{Medical Advice:  Medical Tests}
$Subtitle{}
$Author{
Editors of Consumer Guide
Chasnoff, Ira J}
$Subject{Medical Test Tests URINALYSIS BLOOD Hematocrit Hemoglobin White
blood cell count Differential Sedimentation rate THROAT
CULTURES CULTURE ELECTROCARDIOGRAM ECG ELECTROCARDIOGRAMS ECGS
electroencephalogram EEG electroencephalograms EEGS LUMBAR PUNCTURE PUNCTURES
spinal tap COMPUTED TOMOGRAPHY CT scanning Cat scan scans}
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Your Child:  A Medical Guide


Medical Tests


     Laboratory tests are used by doctors to help identify illnesses, to
determine what particular type of infectious organism is causing a problem,
and to learn how serious a disease may be.  Some procedures can be performed
right in the doctor's office; others must be done in a laboratory, where more
complex equipment is available.  Some common tests and procedures are
described here.

URINALYSIS

     Urinalysis means analysis of a specimen of urine (the liquid form of body
waste).  Urine tests can reveal infections in the kidneys, the bladder, and
the rest of the urinary tract.  The chemical and cell content of urine can
also show how well the digestive system is working.
     Urine can be tested in four different ways.  First, it can be examined
visually for color and texture.  Normal urine is a clear yellow; if it is
cloudy, reddish, or some other color, an infection or an injury may be present
in the body.  Second, the water content of the urine can be measured.  This
shows how well the kidneys are doing their job of filtering the body's wastes.
Third, the chemical content of the urine can be analyzed, to find out if the
body is discarding necessary chemicals that should be retained.  Finally, the
urine can be examined under a microscope to find out what cells, bacteria, and
other material are present.
     Chemical analysis of urine is often used as a screening test for
diabetes, a disease in which the body does not properly use the carbohydrates
(sugars and starches) that are its chief sources of energy.  To test for
diabetes, the amount of glucose (a form of sugar) in the urine is measured by
dipping a chemically treated stick in the urine and comparing the color of the
stick with a color chart.  If the glucose concentration is above a certain
level, diabetes may be the cause.  Blood tests are then done to verify the
diagnosis.

BLOOD TESTS

     Blood circulates throughout the body, so the contents of the blood can
provide information both about general health and about specific diseases.
The blood to be tested is drawn out of a vein with a syringe or taken by
pricking a finger.  The method used to take a sample depends on how much blood
is needed for the tests that are to be done, and also how "clean" the specimen
needs to be.  A finger-stick sample is more likely to be contaminated by
contact with the surface of the finger than is a sample taken by putting a
sterile needle into a vein.
     Many different tests can be done on the blood, and a few of the most
common ones are described here.  More complex tests can be done to find out
what chemicals are present in the blood.

     Hematocrit

     This test is done to find out how much of the blood is made up of red
blood cells, which carry oxygen to the body tissues.  This is one of two tests
done to check for anemia (red blood cell deficiency).  A blood sample is spun
in a machine called a centrifuge, which makes it separate into red blood
cells, white blood cells, and plasma.  The red cells are the heaviest, so they
sink to the bottom.  The percentage of red cells is then determined and
compared with the normal range.

     Hemoglobin

     Hemoglobin is a protein that gives red blood cells their red color; it
combines with oxygen so that it can be carried in the blood.  The amount of
hemoglobin in the blood is tested by adding certain chemicals to the blood and
then measuring the intensity of the red color that signifies the presence of
hemoglobin.  A hemoglobin test is often done at the same time as a hematocrit.
(This is the other test always done to check for anemia.)

     White blood cell count

     White blood cells play a role in the body's defense against infection.
Too many or too few of these cells in the blood may indicate an infection or a
disorder.  To count the white blood cells, a blood specimen is diluted and put
in a counting chamber, which is a slide with a grid on it.  The slide is
examined under a microscope, and the cells are counted.  This test can be done
in most doctors' offices.

     Differential blood cell count

     There are five different types of normal white blood cells; each type has
a distinctive shape and appearance, and each one has a different function.  To
get more precise information about a disease, the doctor may need to know how
many of each type of white blood cells are present in the blood.  To do this,
a stain is added to a blood specimen; because the stain affects each type of
white blood cell differently, it is then easier to tell them apart.  The
stained specimen is examined under a microscope, and at least 100 white blood
ceils are identified and classified.  The cells are also examined to see if
they have a normal shape.  In the course of this test, the red blood cells can
also be counted and checked for abnormalities.

     Sedimentation rate

     The sedimentation rate reflects the speed at which red blood cells move
through the blood and settle in the bottom of a container.  To test the rate
of settling, a chemical is added to a blood sample to keep it from clotting.
Then the red cells are timed as they move to the bottom of a specially marked
test tube.
     This test is used to screen for diseases.  A rapid sedimentation rate is
a sign of disease, but the test does not identify what is causing the cells to
fall more quickly than normal.  Keeping track of the sedimentation rate in
successive tests can help a physician follow the progress of diseases that
cause inflammation, including rheumatic fever and rheumatoid arthritis.

THROAT CULTURES

     A throat culture is done to find out if a throat infection is being
caused by bacteria and, if so, to identify the specific type of bacterium.
This can provide the doctor with important information.  If the infection is
due to a virus rather than to a bacterium, the doctor will know not to
prescribe antibiotics (viruses don't respond to antibiotics); if a bacterium
is the cause, knowing which one it is will enable the doctor to prescribe the
correct antibiotic to combat it.
     To collect material for the culture, the doctor uses a cotton-tipped swab
to remove cells and discharge from the throat.  This material is put into a
growth medium (a special substance that encourages bacteria to grow).  The
specimen is watched carefully, and the bacteria are identified.  Because
throat cultures are often sent to a laboratory for analysis, it may take 48
hours to get the results.

OTHER CULTURES

     Although throat cultures are the most commonly performed, cultures can
also be made from blood, bowel movements, and urine, as well as from discharge
coughed up from the lungs or obtained from an infected eye or ear or an
infected cut or wound.  As with a throat culture, material from the site is
sent to a laboratory, where it is placed in a growth medium to see what types
of bacteria grow.

ELECTROCARDIOGRAM

     An electrocardiogram, or ECG, is a recording of the electrical impulses
of the heart.  These impulses are what make the heart beat in a regular
rhythm.  To make such a record, the patient is attached to an ECG machine with
electrodes (metal plates that are placed on the arms, legs, and chest).  These
electrodes pick up the electrical impulses that move through the body.  The
impulses cause a needle in the machine to move on a piece of paper as the
paper moves through the machine.  Where the needle touches the paper, it makes
a line.  The physician studies the pattern on the paper to see if the heart
rhythm is normal.
     The ECG does not hurt the patient, but it is important for the patient to
stay very still while the recording is being done.  All muscle movements, not
just movements of the heart muscle, are caused by electrical impulses.
Therefore, any movement can affect the ECG recording and give an inaccurate
picture of the heartbeat.
     An ECG is done to check for arrhythmias (irregular heart rhythms), an
enlarged heart, heart valve disorders, heart malformations, and many other
heart disorders.  The test can be done in a doctor's office or an outpatient
laboratory.

ELECTROENCEPHALOGRAM

     An electroencephalogram, or EEG, is a recording of electrical activity in
the brain.  It is a painless procedure similar to an ECG.  The metal plates
known as electrodes are attached to the patient's head and to an EEG machine.
The electrodes pick up the brain's electrical impulses.  These impulses
activate a needle, which traces the pattern of the impulses on a piece of
paper moving through the machine.  The physician compares the pattern on the
recording with patterns of normal brain activity and determines if there is an
abnormality.  Recordings from opposite sides of the brain can also be compared
to see if the patterns match.
     An EEG is done to test for epilepsy, brain tumors, encephalitis
(inflammation of the brain), and other brain disorders.

LUMBAR PUNCTURE

     A lumbar puncture, or spinal tap, is the method used to obtain a sample
of cerebrospinal fluid for testing.  Cerebrospinal fluid is a clear liquid
that surrounds the brain and the spinal cord.  In a lumbar puncture, a needle
is used to penetrate into the lumbar spine (the lower portion of the spine)
between two vertebrae (the bones that make up the spine) and to draw out some
fluid.  The pressure in the spinal column can be measured at the same time.
The fluid is examined to see if it is clear or cloudy and to see if it
contains any blood.  It is then tested for viruses, bacteria, and other signs
of infection.
     A lumbar puncture may be done to test for meningitis, encephalitis, brain
hemorrhage (bleeding in the brain), polio, and other nervous system disorders.
Under the usual circumstances, there is no risk from a lumbar puncture.  If
the spinal fluid is under extreme pressure, however, the procedure carries
some risk of complications; a different technique is then used to minimize
risk.

COMPUTED TOMOGRAPHY

     Computed tomography, or CT scanning, is a sophisticated x-ray study.  A
series of x-ray films is made of a part of the body, such as the head or the
torso.  The patient is placed in a tunnel-like opening in the scanning
machine.  He does not have to be repositioned for each picture, as he would
for ordinary x-ray films, because the scanning machine is capable of taking
x-ray images from many different angles.  A computer then assembles those
x-ray images into cross-sectional pictures of that part of the body.
     CT scans are used to find abnormal growths or other problems in areas
that are inside the body and therefore impossible to see without potentially
dangerous exploratory surgery.  For example, the brain can be examined for an
abnormal growth without opening up the skull.
     CT scans are usually done in a hospital.  The equipment for the procedure
is expensive, and a limited number of scanners are available.  Sometimes a
patient must be transported to another hospital, or even to another town, for
this test because a scanner is not available in his or her hometown.