Diseases related to platelets and coagulation proteins.
Bleeding disorders. Disorders of platelet number
Reduction in the number of blood platelets (thrombocytopenia)
may be the result of impaired production or increased
destruction of platelets. Normal platelet counts are
between 150,000 and 400,000 per cubic millimetre. When
the platelet count drops to 50,000 to75,000, and particularly
to 10,000 to 20,000, spontaneous bleeding may occur.
Thrombocytopenia is associated with such blood diseases
as aplastic anemia and leukemia and is attributed to
impaired production of platelets. Similarly, excessive
irradiation, exposure to certain chemicals (such as
benzene), or medications used in cancer chemotherapy
decrease the production of platelets. In sensitive persons
drugs such as quinidine provoke platelet antibodies
and platelet destruction, resulting in thrombocytopenia.
Thrombocytopenia also may accompany certain infections
such as measles and autoimmune disorders such as systemic
lupus erythematosus and idiopathic thrombocytopenic
purpura.
Thrombocytopenia, if sufficiently severe, is accompanied
by spontaneous bleeding from the capillaries. This causes
the appearance of tiny purplish spots (petechiae) or
larger black and blue areas (ecchymoses) in the skin.
Bleeding occurs commonly from the nose and gums and
occasionally from sites such as the urinary tract and
the intestines; hemorrhage in the brain can have serious
consequences.
