ANEMIA Definition



Anemia represents a decrease in red cell mass or hemoglobin content of blood below physiolog­ical need as set by tissue oxygen demand. The conventional limits for normal range of hemoglo­bin represent the values obtained for 95 per cent of a normal, healthy population, assuming a nor­mal distribution of individuals (Table 51-1). In physiological terms, different ranges exist for men and women, for infants and growing children, and for different metabolic states. Anemia is an expression of many pathological conditions and is not itself a disease state but a clinical sign of such disorders. Therefore, analysis of any anemia should follow a tripartite logical pathway: (1) seek mechanisms by which the anemia occurs, e.g., bleeding, lack of red cell production, or excessive red cell destruction; (2) identify associated diseases that cause anemia; (3) evaluate morpholog­ically the peripheral blood smear.

Determinants of the normal range for hemoglo­bin, hematocrit, and red cell count include age, sex, and ambient altitude. Newborn infants have high values, which soon decline with rapid growth in infancy. Prepubertal boys and girls have similar values. At puberty, male sex hormones produce a rise in erythropoiesis so that adult males have hemoglobin levels approximately 2 to 4 gm/dl higher and hematocrits 5 to 7 per cent higher than adult females. The healthy elderly normally suffer no decline in hemoglobin or he­matocrit values; however, because of increased in­cidence of chronic diseases, elderly populations may show slight decreases in these values. Pop­ulations living at altitudes over 4000 feet above sea level show increased hematocrits, which ap­pear to represent physiological adaptation to the desaturation resulting from diminished atmos­pheric oxygen tension.