lation. The spleen partially dismantles the erythro-
cytes, reducing toxic heme into BILIRUBINthat the
body excretes with the BILE. The LIVERthen recy-
cles these components for numerous other uses in
the body. Accelerated hemolysis, which results in
ANEMIA, can occur with, or characterizes, various
disorders.
CONDITIONS IN WHICH HEMOLYSIS MAY OCCUR
adverse DRUGreactions BLOODenzyme disorders
BLOOD TRANSFUSIONreaction ERYTHROCYTEmetabolic
HEMOGLOBINdisorders disorders
SEPTICEMIA IMMUNE SYSTEMdysfunction
SYSTEMIC LUPUS ERYTHEMATOSUS SICKLE CELL DISEASE
(SLE) THALASSEMIA
See also APOPTOSIS; CELL STRUCTURE AND FUNCTION;
PHAGOCYTOSIS; SPLENOMEGALY.
hemophilia A group of inherited GENETIC DISOR-
DERSin which certain CLOTTING FACTORSare defi-
cient or absent, resulting in clotting dysfunction.
People who have hemophilia tend to bleed easily
and longer than normal. Some forms of hemo-
philia carry substantial risk for life-threatening
hemorrhage (bleeding).
Types of hemophilia Doctors classify hemo-
philia according to the deficient clotting factor,
which may be missing from the BLOOD, present in
subnormal quantities, or present but defective.
About 85 percent of people who have hemophilia
have hemophilia A, a deficiency of clotting factor
VIII (also called antihemophilic factor A). The
remaining 15 percent have hemophilia B, a defi-
ciency of clotting factor IX (also called Christmas
factor, antihemophilic factor B, or PLASMAthrom-
boplastin). Hemophilia B was once called Christ-
mas disease—named after the family in which
doctors first identified the clotting factor IX defi-
ciency—and distinguished this type of hemophilia
from the classic hemophilia A. Hemophilia C,
which is very rare in the United States, is a defi-
ciency of clotting factor XI (also called plasma
thromboplastin antecedent).
Inheritance patterns The most common types
of hemophilia, hemophilia A and hemophilia B,
are inherited X-linked CHROMOSOMAL DISORDERS,
meaning they nearly always only affect males. The
daughters of a man who has hemophilia A or B
will all carry the defective GENE, though the sons
will have normal clotting factor genes. The son of
a carrier has a 50 percent chance of having hemo-
philia; the daughter of a carrier has a 50 percent
chance of also carrying the defective genes. Rarely,
hemophilia A or B occurs through spontaneous
gene MUTATION. In such circumstances it is possible
for a woman to have the disorder. Hemophilia C,
which primarily affects people who are of Ashke-
nazi Jewish descent, is an autosomal disorder that
affects men and women equally though is very
rare.Symptoms and Diagnostic Path
Excessive bleeding is the most common symptom
of hemophilia A or B, which often first manifests
after CIRCUMCISION. The more severe the hemo-
philia, the earlier in life symptoms become appar-
ent. Some men may not experience symptoms
until adulthood, while others experience life-
threatening hemorrhage with common childhood
injuries such as nosebleed (EPISTAXIS) and trauma
such as a cut. The diagnostic path includes blood
tests that measure clotting times, PLATELET AGGRE-
GATION, blood cell counts, and the presence of clot-
ting factors VIII, IX, and XI, and the von
Willebrand factor. The findings of these tests,
along with personal and family medical histories,
are generally conclusive of the diagnosis.
The amount of functional clotting factor in the
blood determines the severity of the hemophilia.
Clotting factor presence above 10 percent gener-
ally produces only mild to moderate symptoms;
clotting factor presence below 1 percent, which
occurs in about 70 percent of people who have
hemophilia, generally produces severe symptoms.
Life-threatening hemorrhage is the most signifi-
cant consequence of hemophilia.Treatment Options and Outlook
The goal of treatment is generally to raise the defi-
cient clotting factor to 30 percent, or 50 to 100
percent during episodes of active bleeding,
depending on the site. Treatment may be transfu-
sions with fresh frozen plasma or plasma cryopre-
cipitate, both of which contain clotting factors VIII
and IX, or with clotting factor concentrates. The
more often these treatments are necessary, how-
ever, the greater the likelihood the person willhemophilia 143