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1.
2. The practice of modern medicine would be impossible without the tests performed by medical
laboratory scientists in the clinical laboratory.
Laboratory scientists analyze body fluids and other medical specimens, providing laboratory data
and vital information to other members of the health care team.
Clinical laboratory tests are used to diagnose, treat, monitor, and prevent disease.
The clinical laboratory includes several specialized disciplines: microbiology, hematology,
immunology, transfusion medicine, clinical chemistry, and molecular diagnostics.
Most hospitalized patients with respiratory disease undergo many laboratory tests, and it is
important for respiratory therapists (RTs) to have a basic understanding of the commonly ordered
tests.
3. Phases of Laboratory Testing
Laboratory testing involves a pre-analytical, analytical, and post-analytical phase.
The pre-analytical phase is related to specimen selection, collection, and transport.
The RT may be involved in this phase, particularly in collection of arterial blood samples and
pulmonary secretions for laboratory testing.
The analytical phase is the actual testing performed by laboratory scientists.
The post-analytical phase involves reporting and interpretation of results.
Most laboratory tests are performed using blood collected from peripheral veins, arteries, or
capillaries.
most tests, the site of blood collection has no effect on the analysis or the results.
4. Exceptions include blood gases and lactic acid that vary significantly by collection site.
Therefore, it is important that appropriate selection, collection, and transport be used.
Blood collection tubes, with various stoppers and additives, must be matched to the analytes being
tested.
Other specimens submitted for laboratory tests include body fluids, secretions such as sputum,
pleural fluid, cerebrospinal fluid, urine, feces, biopsy material, and sweat.
5. Composition of Blood
Blood consists of two major components: the formed elements (45%) and the plasma (55%).
The formed elements are composed of three types of cells: white blood cells (leukocytes), red
blood cells (erythrocytes), and platelets (thrombocytes).
These formed elements are made in the bone marrow from stem cells. The plasma consists of
water and soluble substances including electrolytes, clotting factors, immunologic factors, proteins,
lipids, and hormones.
Almost every substance the cells use must be transported by the plasma.
Serum is the fluid remaining when the blood is allowed to clot.
Test results can be affected by hemolysis, storage times and temperature, method of transport,
interfering conditions of the blood (icterus, lipemia, turbidity), inadequate blood volume when
using tubes with additives, and using the wrong collection tube.
6. The usefulness of a test is evaluated in terms of its predictive value model, which includes
measurements of clinical sensitivity, clinical specificity, positive predictive value, and negative
predictive value
Sensitivity: frequency of positive test results of patients with disease. Example: A sensitivity of
98% means that 98% of the patients with the disease will be detected by the test (TP), and 2% of
the patients with the disease will be negative with the test (FN).
Specificity: frequency of negative test results of patients without disease. Example: A
specificity of 98% means that 98% of the patients without the disease will be negative for the test
(TN), and 2% of the patients without the disease will be positive for the test (FP)
7. Hematology
Clinical laboratory tests in hematology can be divided into two main categories:
(1) general hematology tests for evaluating normal and abnormal blood cells and
(2) coagulation studies for evaluating blood clotting.
Complete Blood Count
The CBC is an overall assessment of the quantity and morphology (appearance) of the white blood cells
(WBCs), red blood cells (RBCs), and platelets.
CBC analyzers examine whole blood using various technologies and software to count cells and assess
their volume and internal structures. However, CBC results are reviewed and verified by laboratory
scientists before they are reported.
8.
9. White Blood Cells
WBCs function as part of the immune system in protecting the body from various pathogenic
microorganisms and foreign antigens.
WBCs originate from hematopoietic stem cells in the bone marrow, develop into specific cell
lineages through the influence of growth factors, and are released into the peripheral blood when
mature.
WBCs that are normally present in the peripheral blood include segmented neutrophils, bands,
eosinophils, basophils, lymphocytes, and monocyte
10.
11. Neutrophils
Neutrophils are produced and stored in the bone marrow, a process that takes 8 to 12 days.
if the demand for neutrophils increases—as may occur in an acute bacterial infection— their time
in the bone marrow may be shortened to as few as 2 days.
In these cases, some immature neutrophils may be released. Once released into the peripheral
blood, neutrophils have a very short half-life of 6 to 8 hours
12. Eosinophils
Eosinophils are a type of granulocyte with large granules that stain bright orange or pink, whereas
basophils have large granules that stain dark blue or purple.
Eosinophils normally constitute 1% to 3% of WBCs,
Eosinophils also accumulate at the site of allergic reactions
basophils
are even more rare at 0% to 1%.
Both cell types are involved in immune system regulation, control of parasitic infections, and allergic
allergic reactions.
13. Lymphocytes
Lymphocytes constitute 20% to 45% of circulating WBCs in adults; in healthy children, the relative
and absolute lymphocyte count is higher.
Lymphocytes are particularly important in the body’s defense against foreign microorganisms and
cells.
There are three major types of lymphocytes: T cells, B cells, and NK (natural killer) cells.
T and B cells participate in the body’s adaptive or specific immune response by recognizing foreign
antigens and tagging them for destruction.
T cells are involved in cell mediated immunity, which is particularly important in eliminating viruses
and other intracellular organisms.
14. Monocytes
Monocytes are the largest WBCs normally seen in the peripheral blood and constitute 2% to 11% of
circulating WBCs.
In tissues, the monocyte is known as a macrophage.
The primary functions of the monocyte are phagocytosis of organisms and other foreign material
invading the body and initiation and regulation of the specific immune response with T
lymphocytes.
In the lung, alveolar macrophages play a key role in clearing inhaled particulate matter
15. Leukocytosis is an increase in the WBC count above the reference range,
leukopenia is a decrease in the WBC count below the reference range
neutropenia. Increases in the cell counts may be primary (a result of uncontrolled proliferation of
cells in the bone marrow) or secondary (a result of stimulation of the bone marrow secondary to
other diseases or disorders)
Neutrophilia is a common response to acute bacterial infections, such as bacterial pneumonia
16. Common Causes of Nonmalignant
or Reactive Neutrophilia
PATHOLOGIC
Acute bacterial infections
Other infections (fungal, parasitic, early stages of viral infections)
Inflammatory responses
Tissue damage (burns, surgery, traumatic injury, myocardial infarction)
Autoimmune disorders
Acute hemorrhage or hemolysis
Metabolic disorders (acidosis, uremia)
Certain drugs, chemicals, or toxins
PHYSIOLOGIC (PSEUDONEUTROPHILIA)
Physical or emotional stress
Strenuous exercise
Exposure to temperature extremes
Epinephrine administration
Anesthesia
17. DECREASED NEUTROPHIL PRODUCTION
Drugs, chemicals, physical agents (e.g., chemotherapy,
benzene, radiation)
Disorders of stem cells, acquired and inherited
Cancers infiltrating the bone marrow
Vitamin B12 or folate deficiency (megaloblastic anemia)
INCREASE IN NEUTROPHIL DESTRUCTION
Overwhelming bacterial infection
Immune disorders (antibody production against neutrophils)
PSEUDONEUTROPENIA
Bacterial endotoxins
Hypersensitivity reactions
18. Eosinophilia (increase in eosinophils) is often seen in parasitic infestations and allergic states (such
as hay fever, dermatitis, and drug reactions). Patients with extrinsic or atopic asthma often have
eosinophilia.
Basophilia (increase in basophils) is usually associated with myeloproliferative neoplasms
Lymphocytosis (increase in lymphocytes) is typically seen in viral infections and certain bacterial
(pertussis) and parasitic (toxoplasmosis) infections. In some viral infections, especially infectious
mononucleosis,
Lymphocytopenia (decrease in lymphocytes) is seen in acquired and congenital immune deficiency
states and in various conditions such as acute inflammation, malnutrition, and after treatment with
chemotherapy, radiation, or corticosteroids.
19. Monocytosis (increase in monocytes) is characteristic of certain infections, including tuberculosis,
syphilis, typhoid fever, and subacute bacterial endocarditis .
blasts, which are the most immature stage of a cell type, accumulate in the bone marrow and
peripheral blood.
These blasts quickly replace all other cells in the bone marrow
Polycythemia vera is characterized by a proliferation of granulocytic, erythrocytic, and platelet
precursors in the bone marrow with an increase in WBCs, RBCs, and platelets in the peripheral
blood.
20. Red Blood Cells
Normal RBCs assume the shape of a biconcave disk to facilitate their primary function of carrying
oxygen and to provide maximal deformability to bend as they pass through small capillaries
RBCs have a life span of approximately 120 days.
Hematocrit (Packed Cell Volume). The Hct is the ratio of the packed RBC volume to the volume of
whole blood.
A manual Hct is performed by centrifuging whole blood to pack the blood cells to the bottom of a
small capillary tube and then measuring the percentage or fraction of the total blood volume
occupied by the RBC
21. Hemoglobin.
Hemoglobin is the protein that carries oxygen to the tissues; it is the major component of RBCs.
Hemoglobin also is important in maintaining acid-base balance by acting as a buffer and by
carrying carbon dioxide (CO2) from the tissues to the lungs.
The hemoglobin molecule consists of four heme groups, each with an iron molecule capable of
binding oxygen, and four globin chains
22. Red Blood Cell Indices. Three erythrocyte indices
are the mean cell volume (MCV),
mean cell hemoglobin (MCH),
mean cell hemoglobin concentration (MCHC).
anemia
is clinically defined by a decrease in the hemoglobin concentration below the reference range for
an individual’s gender and age
Patients with anemia have a decreased oxygen-carrying capacity of the blood. The response to
severe and chronic anemia is vasodilation, which increases demands on the heart to maintain
blood pressure and can result in high-output cardiac failure
23. Polycythemia is an increase in the RBC count, hemoglobin, and Hct and may be
primary, secondary, or relative (spurious).
Primary polycythemia is uncommon and is caused by an uncontrolled proliferation of
hematopoietic cells within the bone marrow. Patients with chronic hypoxemia may develop a
secondary
polycythemia to compensate for the reduction in blood oxygen levels; polycythemia can increase
cardiac workload and the incidence of thrombosis
24. Reticulocyte Count:
The reticulocyte is the final erythrocyte development stage before the RBC is fully mature.
reticulocyte count is performed by obtaining the percentage of reticulocytes among the RBCs.
Normally about 1% of the circulating RBCs are reticulocytes, with slightly higher values in
newborns.
25. Platelet Count
Platelets are the smallest cells in the peripheral blood.
After injury to a blood vessel, they participate in clot formation at the site of the injury to stop the
bleeding.
The platelet count routinely is provided as part of the CBC
Thrombocytopenia A reduction in the platelet count below the reference range
Thrombocytosis An increase in platelets
26. Erythrocyte Sedimentation Rate
Although not part of the CBC, the erythrocyte sedimentation rate (ESR) is a commonly ordered test
to monitor
inflammatory diseases. If whole blood is placed in a vertical tube, the RBCs tend to fall to the
bottom.
27. Coagulation Screening Tests
Hemostasis (ability to prevent hemorrhage, form a blood clot, keep blood flowing in circulation)
the APTT, and the PT/INR.
The APTT assesses the clotting factors in the intrinsic and common pathways by measuring the length of
time required for plasma to form a fibrin clot once the intrinsic pathway is activated.
The reference range varies by laboratory but is usually about 25 to 35 second
The reference range for the
PT generally falls between 12 and 15 seconds.
An INR is calculated from the PT result using a formula that takes into account the specific reagents and
instrument used for the test.
The INR should be between 2.0 and 3.0 in patients taking warfarin who have atrial fibrillation or a history
of pulmonary emboli and generally between 2.5 and 3.5 in patients with a mechanical heart valve.
28. D-dimer.
D-dimer is produced as a result of the breakdown of fibrin clots that form in the vasculature.
The upper reference range for D-dimer in the plasma is about 240 ng/mL, but the value varies
depending on each laboratory’s methods.
An increase in D-dimer is nonspecific and can be observed in many conditions with excessive
clotting, as well as in inflammation, renal disease, and even pregnancy.
D-dimer test has high sensitivity, a level below the upper limit of the reference range can help rule
out both systemic thrombosis, such as disseminated intravascular coagulation, and local
thrombosis, such as pulmonary embolism and deep vein thrombosis.
