The anemias
Anemia varies in severity, and the tolerance of different
persons for anemia varies greatly, depending in part
upon the rate at which it has developed. When anemia
has developed gradually, affected persons may endure
severe grades of anemia with few or no complaints, whereas
rapidly developing anemia causes severe symptoms; if
sufficiently severe and rapidin development, anemia
can be fatal. In anemia the blood is capable of carrying
only a reduced amount of oxygen to tissues, a condition
that stimulates the lungs to increase the respiratory
rate in order to pick up more oxygen and the heart to
increase its rate (pulse) in order to increase the volume
of blood delivered to the tissues. Associated complaints
include a pounding headache due to the increased blood
flow.
Anemia is always a sign, either predominant or incidental,
of some underlying congenital condition or acquired
disease. There are many varieties of anemia. Their clinical
manifestations are generally similar, and yet they must
be differentiated because their causes differ, and consequently
their treatment is not the same. Differentiation is
based on the history and physical examination, which
may reveal an underlying cause, and on examination of
the blood. The latter includes measurement of the degree
of anemia and microscopic study of the blood cells.
If the number of red cells, the hemoglobin concentration
of the blood, and the volume of packed red cells are
known, the mean volume and hemoglobin content can be
calculated. The mean corpuscular volume (MCV) normally
is 82 to 92 cubic micrometres, and about a third of
this is hemoglobin (mean corpuscular hemoglobin concentration,
MCHC, normally is 32 to 36 percent). If determined accurately,
the MCV and the MCHC are useful indexes of the nature
of an anemia.
Under the microscope the red cells of humans appear
as round biconcave disks of uniform size with an average
diameter of approximately 7.8 micrometres, or 0.0078
millimetre (a common pin is about one millimetre thick).
Microscopic inspection of films of blood dried on glass
slides and stained with aniline dyes allows observation
of variations in the size and colour and other abnormalities
of individual red cells and also permits examination
of the white cells and platelets
