Webster's New World Medical Dictionary

hemangiosarcoma
See 
angiosarcoma.
hemarthrosis
Blood in a joint.
hematemesis
Bloody vomit.
hematocrit
The proportion of the blood that
consists of red blood cells. Abbreviated Hct. Hct is
expressed as a percentage. For example, an Hct of
25 percent means that there are 25 milliliters of red
blood cells in 100 milliliters of blood. The normal
ranges for Hct depend on the age and, after adoles-
cence, the sex of the patient. The normal ranges are
40.7 to 50.3 percent in adult males, and 36.1 to
44.3 percent in adult females. The values returned
on Hct tests may vary slightly between laboratories.
An abnormally low level of Hct is referred to as ane-
mia and can come from bleeding, iron deficiency,
breakage of red blood cells (hemolysis), and many
other causes. An abnormally high level of Hct is
referred to as polycythemia and can be a result of
chronic lung disease, polycythemia rubra vera, and
other causes. See also 
CBC.
hematologist
A physician who specializes in
diagnosing and treating diseases of the blood.
hematology
The branch of medicine concerned
with the blood and blood-forming tissues, encom-
passing the diagnosis and treatment of disorders of
the coagulation process, blood-cell formation,
hemoglobin synthesis, and immune system, as well
as cancers of blood and blood-forming organs such
as leukemias and lymphomas.
hematoma
A localized swelling that is filled with
blood caused by a break in the wall of a blood ves-
sel. The breakage may be spontaneous, as in the
case of an aneurysm, or caused by trauma. The
blood is usually clotted or partially clotted, and it
exists within an organ or in a soft tissue space, such
as muscle. Treatment depends on the location and
size of the hematoma but usually involves draining
the accumulated blood. A hematoma in or near the
brain is particularly dangerous.