Blood diseases. Introduction

abnormal condition that involves the corpuscular elements of the blood—red cells, white cells, and platelets—and the tissues in which they are formed—the bone marrow, the lymph nodes, the spleen (i.e., the hematopoietic system). This definition, however, needs expansion and modification. In certain types of illness (e.g., pneumonia, appendicitis) the number of leukocytes is increased. This is called leukocytosis and is a physiological response rather than a disease of the blood. In other diseases, as will be mentioned below, a reduction in the number of red cells in the blood (anemia) occurs; such anemia isnot usually thought of as representing a “blood disease,” but it does represent the response of the hematopoietic system to the underlying disease. Strictly speaking, the term blood disease refers only to those types of anemia and those disorders of leukocytes, of platelets, of coagulation, and of the bone marrow, lymph nodes, and spleen in which the blood-forming organs or coagulation systems are the primary sitesinvolved.

In the following, all varieties of alteration in the three corpuscular elements of the blood will be discussed. For convenience, disorders chiefly affecting the red cells, the leukocytes, the platelets, and the process of blood coagulation will be considered in turn, but, as will becomeapparent, alterations in disease do not necessarily occur in only one of these groups of bloodcells; in its reactions in disease the hematopoietic system may demonstrate multiple changes.

Since the blood circulates throughout the body and carries nutritive substances as well as waste products, examination of it can be important in detecting the presence of disease. Examination of the blood may be considered in two categories; namely, the analysis of the plasma and the study of the corpuscles. Examination of the plasma includes measurement of plasma proteins, blood sugar, salts (which, being in solution and in the ionic state, are referred to as electrolytes), lipids, enzymes, urea, and various hormones. Such measurements are useful in the identification of diseases that are not classified as blood diseases—e.g., diabetes, kidney disease, and thyroid disease. Special studies of plasma or its components can be carried out to determine the status of blood clotting.

Long before the nature and composition of blood were known, a variety of complaints were attributed to disordered blood. The red cells were not recognized until the 17th century, and it was another 100 years before one of the forms of the white cells, the lymphocyte, and the clotting of blood were described. In the 19th century other forms of leukocytes were discovered, and a number of diseases of the blood and blood-forming organs were distinguished.

In the 19th century and also in the first quarter of the 20th century much attention was given to descriptions of the morphological changes—the changes in form and structure—that take place in the blood during disease and to the signs and symptoms of the various blood diseases. In the years that followed, a more physiological approach began to develop, concerned with the mechanisms underlying the development of disease and with the ways in which abnormalities might be corrected. Following World War II, progress was greatly accelerated by the strong financial support that medical science received during a particularly productive age of medical research.

The study of a particular instance of disease involves inquiry into the circumstances of its development, the symptoms, and the course of the illness (the history). A thorough physical examination of the affected person and specific laboratory tests are essential.

In the case of the blood, certain features of the physical examination are especially important in diagnosis. These include noting the presence or absence of pallor or, the opposite, an excess of colour; jaundice, red tongue, enlargement of the heart or liver; the presence or absence of small purple spots or larger bruises in the skin; enlargement of lymph glands (nodes); enlargement of the spleen; and tenderness of the bones.

Laboratory studies particularly valuable in diagnosis include (1) determination of the numberand characteristics of red cells in the blood; i.e., the existence of anemia or polycythemia, (2)study of the white cells, their number and their proportions as to type, (3) enumeration of the blood platelets and a study of the blood-clotting process, and (4) in many instances a study of the bone marrow. It is sometimes necessary to remove a lymph node for microscopic examination, and X-ray examinations may be necessary for the detection of organ or lymph node enlargement or bone abnormalities. The more unusual cases may require further examinations—e.g., special serological (serum-related) or biochemical procedures or various measurements using radioactive isotopes to outline an organ or quantitate blood volume.