Download Overview of the Medical Laboratory

Slide 1
Under the Microscope 101
An Introduction to Pathology and Laboratory Medicine
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Careers in Pathology and Laboratory Medicine
A highly skilled team of pathologists and medical laboratory scientists, technicians and
specialists play a critical role in evaluating information needed to give the best care to
an ill or injured patient. In fact, more than 70 percent of medical decisions made by
physicians are based on laboratory findings. Some of the professionals who work in
medical laboratories include the:
Pathologist
A pathologist is a medical doctor who examines tissues and is responsible for the
accuracy of laboratory tests. The pathologist and the patient’s doctor consult on
which tests to order, interpretation of test results, and appropriate therapy.
Medical Laboratory Scientist and Medical Laboratory Technician
Medical laboratory scientists and Medical laboratory technicians perform tests in all
areas of the medical laboratory. They are also responsible for confirming the accuracy
of test results and operating complex electronic equipment.
Cytotechnologist
Cytotechnologists examine human cell samples under the microscope for early signs
of cancer and other diseases. The cytotechnologist analyzes subtle cell changes and
compares these changes to normal cell findings for that body site.
Histotechnologist and Histotechnician
The Histotechnologist and Histotechnician prepare small sections of body tissues for
microscopic examination by a pathologist. The laboratory professionals work closely
with the pathologist to process tissue biopsies removed during surgery.
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Phlebotomy Technician
The Phlebotomy Technician collects blood samples from patients for analysis in the
laboratory. The laboratory depends on the phlebotomy technician to collect
specimens properly from the patient to produce high quality, accurate laboratory test
results.
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Departments in the Medical Laboratory
Most medical laboratories are divided into distinct departments that separate the types
of tests performed based on sample type and intended result. The major areas and
their functions are:
Clinical Chemistry
The clinical chemistry department performs hundreds of quantitative analyses on a
variety of body fluids. Common chemistry procedures include testing for glucose,
cholesterol, hormones, and electrolytes.
Blood Bank (Immunohematology)
The blood bank provides blood typing and compatibility testing for both donors and
recipients and ensures the safety of the blood supply.
Immunology/Serology
Immunologic/serologic testing evaluates antibodies and/or antigens that may be
indicative of many types of infectious disease. This is important in not only
confirming a diagnosis, but also in treating and managing various conditions.
Microbiology
The microbiology section identifies microorganisms that may be causing disease
(pathogens). The microbiology department also provides information regarding
appropriate antibiotics to use as treatment for various pathogens.
Urinalysis
The urinalysis department screens urine samples for evidence of kidney disease or
bladder infections.
Coagulation
Coagulation procedures are performed to identify possible bleeding or clotting
disorders. Coagulation testing is also used to monitor anticoagulant therapy.
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Hematology
They hematology department performs tests that are important in diagnosing many
disorders such as anemia and leukemia.
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Complete Blood Count
One of the most useful and commonly ordered hematology tests is the complete
blood count (CBC). The CBC includes the number of white blood cells (WBC), red
blood cells (RBC), and platelets as well as the measurement of hemoglobin and
hematocrit. These measurements are performed using sophisticated instruments. The
CBC also includes the percentage differential count of the white blood cells. The
differential is performed on a carefully prepared and stained blood smear using either
venous blood or blood from a fingerstick. A drop of blood is put on a glass
microscope slide and spread out using another slide. The smear is allowed to dry and
then stained using a special hematological stain which allows the various components
of the blood to stain differently from each other. The staining may be done by hand
but is more commonly done in an automated staining instrument. The most common
type of stain in use today is Wright’s stain. The stained smear is then evaluated by the
medical laboratory scientist or medical laboratory technician using the microscope.
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Blood Cells
The following discussion and images describe and illustrate some of the types of cells
normally seen on a differential blood smear.
I. Leukocytes: white blood cells
A. Granulocytes: destroy bacteria and other bloodstream invaders. There are
three subtypes of granulocytes. They were named for the dye color they take
up when stained with Wright’s stain.
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Slide 6
1. Segmented neutrophils are the oldest cells in the granulocytic series
and are the most common leukocyte seen in the blood of a normal adult.
They are characterized by 2 to 5 connected lobes in the nucleus, and
stain dark with thick strands of chromatin. The cytoplasm is pink with
fine pinkish-tan granules.
2. Eosinophils have granules that take up the red dye eosin. They are
characterized by large red to reddish-orange granules which are uniform
in size and shape.
3. Basophils have granules that take up the blue (basic) dye. They are
characterized by blue-black granules that vary in size and number and
usually obscure the nucleus.
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B. Lymphocytes have a very dark nucleus, a clumped nuclear chromatin
pattern, and very little cytoplasm (dark blue). They are usually slightly larger
than a mature red blood cell. There are several classes and functions of
lymphocytes -- the primary functions being production of antibodies and
developing cellular immunity. Lymphocyte subclasses are not distinguishable
on the differential smear.
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C. Monocytes are the largest of the normal white blood cells. They are
characterized by an irregular, folded, or horseshoe shaped nucleus, with lighter
(lavender) staining chromatin. The cytoplasm is sometimes foamy, and it may
contain holes known as vacuoles. Monocytes, like granulocytes, are involved in
destruction of bloodstream invaders. This type of WBC is increased when
bacterial infections or monocytic leukemia are present. In addition, monocytes
are found in tissue where they are known as macrophages.
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Slide 9
II. Erythrocytes are commonly known as red blood cells. They appear as biconcave
discs. They contain hemoglobin and function to carry oxygen to tissues.
Slide 10
III. Thrombocytes are commonly known as platelets. They are small cells (even
smaller than red blood cells) with bits of blue or purple cytoplasm and no nuclear
structure. The primary function of platelets is in blood clotting processes.
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Abnormal Blood Cells
Abnormal differential blood smears may indicate a variety of disease states.
Slide 12
Infection: Mononucleosis
The differential blood smear may demonstrate the presence of a bacterial or viral
infection. This image shows a reactive lymphocyte as it might appear in infectious
mononucleosis. The lymphocyte shows a characteristic cytoplasm with a dark blue
border.
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Sickle Cell Anemia
Sickle cell anemia is characterized by abnormally shaped, "sickled" red blood cells. It
is a genetic disorder, primarily found in the African-American population. An
individual who inherits a sickle cell gene from both parents (homozygous) will have
the severe anemic disease. If the gene is inherited from only one parent
(heterozygous), the individual has the sickle cell trait, but not the anemic state.
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Slide 14
Leukemia
Leukemias are characterized by increased proliferation of white blood cells. A variety
of leukemias are classified on the basis of the cell type affected. This image illustrates
chronic granulocytic (myelogeneous) leukemia. It affects the granulocytes, increasing
the younger cells in the granulocytic series. Very young cells, which are normally only
seen in the bone marrow, may be seen in the peripheral blood smear.
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Identifying Microorganisms
Laboratory professionals also work closely with doctors, nurses, and other members
of the health care team to diagnose and manage diseases that are caused by
microorganisms - bacteria, viruses, parasites, and fungi. In the microbiology
laboratory, they analyze and identify these microorganisms and report the results to
the physician for use in treating the patient. In many cases, the doctor must rely on
the medical laboratory scientist's identification of the microorganism to select the best
treatment.
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Bacteria
The appearance of the microorganism on an agar plate or in the liquid media gives the
medical laboratory scientist preliminary clues to the identity of the microorganism.
After observing the bacterial colonies in the agar plate, the next step in the
identification is to look at the microorganism through the microscope. The
microorganisms are placed on a glass slide and stained with a special stain called a
Gram stain. In a Gram stain, the bacteria will appear gram-positive (purple staining)
or gram-negative (pink staining) depending on the structure of the cell wall. The
Gram staining reaction plus the shape of the individual microorganisms are important
first steps in identification. The two most common shapes are cocci and bacilli. Cocci
are round-shaped cells and bacilli are bacteria with short, rectangular shapes.
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Slides 17 and 18
Bacteria, continued
Notice that both gram-positive cocci (Slide 17) and gram-negative bacilli (Slide 18) are
much smaller than blood cells. Once the pathogenic bacteria are isolated and
identified, the medical laboratory scientist will test the bacteria to determine which
antibiotics will be effective for treating the infection. Antibiotics work against bacteria
by causing irreversible damage to their cell walls or by preventing their multiplication.
These drugs work together with the body's natural disease-fighting forces to eliminate
the pathogens. Since bacteria are living microorganisms, they can develop resistance
to antibiotics; therefore, each bacterium is tested for susceptibility to a variety of
antibiotics.
Slide 19
Viruses
Viruses cannot be grown on regular plate media because they can only reproduce in
living cells. This group of microorganisms is grown in living tissue cultures. The cells
are inoculated with the patient's specimen, such as blood or urine, and are then
incubated. The cells are kept moist and given nutrients by adding liquid growth
media.
Slide 20
Fungi
The oval cells in this slide are not bacteria. They are a form of fungi called yeast which
reproduce by budding. Usually humans are not bothered by yeast because yeast is part
of our body's normal flora. However, when the body's immune system is not working
properly, or if antibiotics are used for a long time, yeast may multiply and cause an
infection. Yeast can cause diaper rash in infants and an oral condition called thrush in
AIDS patients.
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Slides 21 and 22
Parasites: Giardia
(Slide 21) Here is a parasite that is spread by drinking contaminated water. Giardia
lamblia lives in the intestines and can cause diarrhea and other intestinal problems.
(Slide 22) Giardia infection is diagnosed by microscopically examining a slide
preparation. When the medical laboratory scientist sees this parasite, a report is sent to
the doctor so that the patient can receive the appropriate treatment for this disease.
Slide 23
Conclusion
Microbiology is just one of many fascinating and constantly changing areas of
laboratory medicine. The medical laboratory scientist is a laboratory detective who
provides the critical identification of not only microorganisms, but atypical blood cells
and other abnormalities that are very important in the diagnosis and treatment of
diseases. Although the medical laboratory is behind the scenes, the professionals who
work in the lab—medical laboratory scientists, medical laboratory technicians,
cytotechnologists, histologic technicians, phlebotomists, and pathologists—make a
vital contribution to health care.
The American Society for Clinical Pathology (ASCP) provides excellence in education, certification,
and advocacy on behalf of patients, pathologists, and laboratory professionals.
We welcome your comments on this presentation. You may contact us at:
American Society for Clinical Pathology
33 W. Monroe St., Suite 1600
Chicago, IL 60603
Phone: 312-541-4999
Fax: 312-541-4998
Toll-free: 800-267-2727
Customer Service: [email protected]
www.ascp.org
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