CLINICAL LAB SCIENEC

330
ESSENTIALS OF CLINICAL LABORATORY SCIENCE
evaluation is the most important tool used to determine the presence of infection
and the severity of a condition, as well as whether an infection is of a viral
or bacterial nature.
White blood cells are also called leukocytes. They are a vital component
of the immune system that is important in responding to infections and
other conditions that might require an immune response, such as an allergic
condition. The total WBC count may be indicative of a medical condition
if it is either above or below the normal or average count for humans. An
increase or decrease in the number of or changes in the morphology (physical
characteristics) of certain types of WBCs may be critical in establishing
a diagnosis of certain illnesses and may lend clues as to the presence of a
disease and general information that might lead to a diagnosis with further
testing.
A total WBC count is not necessarily indicative of the severity of a disease,
since some serious ailments may show either a low or an elevated white cell
count and counts may vary widely among individuals. Following the determination
of the total WBC count, a differential count from a stained smear is
necessary to determine any changes in the physical characteristics of the WBCs
and the percentages of the several types normally in the circulating blood.
A WBC differential consists of an examination of a thin smear to determine
the percentages of a number of different types of WBCs. White cells may also
invade other body fluids outside the blood system, so it is sometimes necessary
to perform a WBC count and differential of the various types of cells from
fluids other than blood. Some of these fluids include specimens such as urine,
cerebrospinal fluid (CSF) and synovial fluids (fluids present around the joints
of the body). Increased percentages of certain WBCs may indicate either a viral
or bacterial infection. An overall decrease in total WBCs may also be indicative
of overwhelming infections, among other conditions or extreme increases in
the total numbers of WBCs may indicate a serious disease such as one of the
forms of leukemia. White cells and the percentage of the types found in both
the blood system and other fluids of the body are significant, as indicated in
Table 13-1.
Table 13-1 Significance of Increases in Types of Leukocytes
Cell Type
Neutrophils (polys)
Eosinophils
Basophils
Lymphocytes
Monocytes
Significance
Increased in bacterial infections
Increased in allergic reactions and parasitic infections
Reactive to infl ammation of a nonspecifi c origin, such as toxins
Increased in viral infections
Increased in respiratory viral infections and, after undergoing
morphological and physiological changes, phagocytize (eat) foreign
bodies during immune responses
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