hematologic disorders

(medicine) A disorder marked by aberrations in structure or function of the blood cells or the blood-clotting mechanism.

Those disorders marked by aberrations in structure or function of the blood cells or the blood-clotting mechanism. Although many other diseases may be reflected by the blood and its constituents, the abnormalities of red cells, white cells, platelets, and clotting factors are considered to be primary hematologic disorders. See also Blood.

Red-cell abnormalities are principally represented by the anemias and polycythemias. The anemias are marked by a decrease in the hemoglobin concentration, and may be due to blood loss or decreased production or excessive destruction of red cells. Polycythemias are disorders characterized by an increase in the numbers of circulating red cells and usually by a concomitant increase in hemoglobin. Secondary polycythemias result from a compensatory increase in the formation of red cells following hypoxia of the bone marrow. Primary polycythemia or polycythemia vera is a chronic and ultimately fatal disease of middle and old age in which there is a gradual increase in the number of red cells and usually an increase in the number of platelets and leukocytes. See also Anemia; Hemoglobin.

In a wide variety of conditions the many forms of white cell present in the circulation, bone marrow, and lymphoid tissues of the body may be altered in form or number. The suffixes -philia and -penia denote increases and decreases, respectively, for the cells named. Leukopenia, neutrophilia, eosinophilia, and pancytopenia are examples of the wide range of possibilities. The absolute or relative increases or decreases of one or more types of leukocytes are often characteristic of certain disease states. There may also be changes in the proportions of the different cells, and immature or atypical forms may be present. The leukemias represent a special kind of malignancy in which there is usually an uncontrolled proliferation of one or more types of leukocytes, often reflected by great increases in the white cell count of the peripheral blood. See also Leukemia.

The hemorrhagic disorders result from a large number of known and unknown causes or contributing factors, often of a diverse nature. A decrease or abnormality of the von Willebrand factor, a reduction in the number of platelets, a qualitative defect in platelets, or a defect in the vascular wall can all result in failure of the primary hemostatic mechanism, with spontaneous bleeding; this is referred to as purpura. Blood vessel damage may occur as a result of direct or indirect damage by microorganisms during infections, as the result of vitamin C deficiency (scurvy), and following hereditary defects in blood vessel development. There are several forms of thrombocytopenia, all of which are characterized by a decrease in thrombocytes or platelets in the circulation. A defect in fibrin or clot formation gives rise to the type of bleeding seen in hemophilia, in which the primary hemostatic plug is formed normally but breaks down several hours or days later owing to lack of adequate fortification by fibrin. Defects in the clotting process that result in excessive bleeding may be due to an acquired or hereditary deficiency or abnormality of a clotting factor, as in hemophilia A or B. See also Hemophilia; Hemorrhage.

Diseases of the blood and blood-forming tissues.