Webster's New World Medical Dictionary

hematopoiesis
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hemoglobin S
The most common type of abnor-
mal hemoglobin, which is found in people with
sickle cell trait and sickle cell anemia. It differs
from hemoglobin A only by a single amino acid sub-
stitution. The S stands for sickle. See also 
anemia,
sickle cell; sickle cell trait.
hemoglobinuria
The presence of free hemoglo-
bin in the urine, which may make the urine look
dark. Normally, there is no hemoglobin in the urine.
Hemoglobinuria is a sign of a number of abnormal
conditions, such as bleeding and paroxysmal noc-
turnal hemoglobinuria.
hemolysis
Breakage of red blood cells. This
occurs to a minor degree normally as red blood
cells age. However, excessive hemolysis is very
abnormal and leads to hemolytic anemia. See also
hemolytic anemia.
hemolytic anemia
Anemia due to the destruc-
tion, rather than underproduction, of red blood
cells. Hemolytic anemia can result from a medica-
tion reaction, from the immune system attacking the
red blood cells (autoimmune hemolytic anemia),
from destruction of blood cells passing through dis-
eased heart valves, and other causes.
hemolytic disease of the newborn
Abnormal
breakup of red blood cells in a fetus or newborn.
Hemolytic disease of the newborn is usually due to
antibodies made by the mother that are directed
against the baby’s red blood cells. It is typically
caused by Rh incompatibility (a difference between
the Rh blood groups of mother and baby).
Symptoms can be mild or severe and may include
generalized swelling (hydrops fetalis), enlargement
of the liver and spleen, jaundice, and anemia.
Severe cases may lead to brain damage and/or
death. Also known as erythroblastosis fetalis.