Porth's Essentials of Pathophysiology, 4e

282

Hematopoietic Function

U N I T 3

TABLE 13-1 Standard LaboratoryValues for Red Blood Cells Test Normal Values

Significance

Red blood cell count (RBC) Men

4.2–5.4 × 10 6 / μ L 3.6–5.0 × 10 6 / μ L

Number of red cells in the blood

Women

Reticulocytes Hemoglobin Men

1.0%–1.5% of total RBC

Rate of red cell production

14–16.5 g/dL 12–15 g/dL

Hemoglobin content of the blood

Women

Hematocrit Men

40%–50% 37%–47% 85–100 dL 31–35 g/dL

Volume of cells in 100 mL of blood

Women

Mean corpuscular volume

Size of the red cell

Mean corpuscular hemoglobin concentration

Concentration of hemoglobin in the red cell

Mean cell hemoglobin

27–34 pg/cell

Red cell mass

Anemia Anemia is defined as an abnormally low number of cir- culating red blood cells or level of hemoglobin, or both, resulting in diminished oxygen-carrying capacity. 5,6 Anemia usually results from excessive loss (bleeding) or destruction (hemolysis) of red blood cells or deficient red blood cell production because of a lack of nutri- tional elements or bone marrow failure. These mecha- nisms serve as the basis for classifying anemia. The effects of anemia can be grouped into three cat- egories: (1) manifestations of impaired oxygen trans- port and the resulting compensatory mechanisms, (2) reduction in red cell indices and hemoglobin levels,

and (3) signs and symptoms associated with the patho- logic process that is causing the anemia. The manifesta- tions of anemia depend on its severity, the rapidity of its development, underlying pathologic mechanisms, and the person’s age and health status. If the onset is slow, the body compensates for the decrease in oxygen- carrying capacity of the blood with increases in plasma volume, cardiac output, and respiratory rate. These changes can largely compensate for the effects of mild to moderate anemia in otherwise healthy individuals but are less effective in those with compromised respiratory or cardiac function. The redistribution of the blood from cutaneous tis- sues or the lack of hemoglobin causes pallor of the skin, mucous membranes, conjunctivae, and nail beds. Tachycardia and palpitations may occur as the body tries to compensate with an increase in cardiac output. Anemias caused by premature destruction of red cells (hemolytic anemias) are associated with hyperbilirubi- nemia, jaundice, and pigment gallstones. Anemias that result from ineffective hematopoiesis (premature death of red blood cells in the bone marrow) are associated with inappropriately high levels of iron absorption from the gut, which can lead to iron overload and eventual damage to endocrine organs and the heart. Laboratory tests are useful in determining the severity and cause of the anemia. The red cell count and hemo- globin levels provide information about the severity of the anemia, whereas red cell characteristics such as size (normocytic, microcytic, macrocytic), color (normo- chromic, hypochromic), and shape often provide infor- mation about the cause of anemia (Fig. 13-8). Blood Loss Anemia The clinical manifestations and red cell changes asso- ciated with blood loss anemia depend on the rate of hemorrhage and whether the bleeding loss is internal or external. With rapid blood loss, circulatory collapse may occur. With more slowly developing blood loss, the amount of red cell mass lost may reach 50% without the occurrence of signs and symptoms. 3

Percent

100

90

80

70

60

50

40

30

20

10

0

Normal C FIGURE 13-7. Hematocrit.The hematocrit measures the percentage of cells in 100 mL of plasma: (A) normal, (B) decreased in anemia, and (C) increased in polycythemia. Anemia Polycythemia A B