Services
Lab
Complete
Blood Count
Also known as: CBC, Hemogram, CBC with
differential
Related tests: Blood smear, Hemoglobin, Hematocrit, Red blood cell
(RBC) count, White blood cell (WBC) count, White blood cell differential count,
Platelet count
** What is being tested?
The Complete Blood count (CBC) test is an automated count of the cells in
the blood. It provides information about the white blood cell (WBC), red
blood cell (RBC), and platelet populations present. This information
includes the number, type, size, shape, and some of the physical characteristics
of the cells. In only a minute or two, the hematology instrument (the
machine that is used to run the test) can measure thousands of RBCs, WBCs, and
platelets and compare them against established normal ranges. Any abnormalities
found are noted, and the clinical laboratory scientist (CLS) running the
instrument then uses his or her expertise and experience to accept the automated
findings and/or target the sample for further analysis.
In
most cases, the automated CBC is very accurate and the test is complete at this
point. If, however, there are significant abnormalities in one or more of
the cell populations, the blood smear test may be performed. In this test,
a drop of blood is placed on a slide, smeared into a thin layer, allowed to dry,
and then dyed with a special stain. A CLS then looks at the slide under
the microscope and is able to evaluate the cells present. Any additional
information is added to that found by the automated count, and all of the
findings are reported to the doctor.
Blood
consists of cells suspended in a liquid called plasma. These cells - the
RBCs, WBCs, and platelets - are produced and mature primarily in the bone
marrow. Under normal circumstances, they are released into the bloodstream
as needed.
** White Blood Cells (WBCs)
There are five different types of WBCs that the body uses to fight
infections or other causes of injury. These types- neutrophils,
lymphocytes, basephils, eosinophils, and monocytes- are present in relatively
stable percentages that may temporarily shift higher or lower depending on what
is going on in the body. For instance, with an infection, there may be a
higher concentration of neutrophils (a "shift to the left").
With allergies, there may be an increased number of eosinophils, and with
leukemia, there may be a much higher percentage of a single type of a cell, such
as a lymphocyte. In this case, the cell may be present in large numbers,
in a mature form and in a variety of immature forms. The CBC determines
whether there are sufficient WBCs present to fight infection, notes when there
are more than expected, and determines the percentages and numbers of each type.
**
Red
Blood Cells (RBCs)
RBCs are reddish in color and shaped like a donut with a thinner section in
the middle instead of a hole. They have hemoglobin inside them, a protein
that transports oxygen throughout the body. The CBC determines whether
there are sufficient RBCs present and whether the population of RBCs appears to
be normal. RBCs are normally all the same size and shape; however,
variations can occur with vitamin B12 and folate deficiencies, iron deficiency,
and with a variety of other conditions. If there are insufficient
deficiency, and with a variety of other conditions. If there are
insufficient normal RBCs present, the patient is said to have anemia and may
have symptoms, such as fatigue and weakness. Much less frequently, there
may be too many RBCs in the blood (erythrocytosis or polycythemia). In
extreme cases, this can interfere with the flow of blood through the veins and
arteries.'
** Platelets
Platelets are special cell fragments that play an important role in blood
clotting. If a patient does not have enough platelets, he will be at an
increased risk of excessive bleeding and bruising. The CBC measures the
number and size of platelets present. With some conditions and in some
people, there may be giant platelets or platelet clumps that are difficult for
the hematology instrument to accurately measure. In this case, a blood
smear test may be necessary.
Back to
Lab
