A CBC includes (1) enumeration of the cellular elements of the blood, (2) evaluation of RBC indices, and (3) determination of cell morphology by means of stained smears. Counting is performed by automated electronic devices capable of rapid analysis of blood samples with a measurement error of less than 2 percent.²⁰

Reference values for the CBC vary across the life cycle and between the genders. In the neonate, when oxygen demand is high, the number of erythrocytes also is high. As demand decreases, destruction of the excess cells results in decreased erythrocyte, hemoglobin, and hematocrit levels. During childhood, RBC levels again rise, although hemoglobin levels may decrease slightly.

In prepubertal children, normal erythrocyte and hemoglobin levels are the same for boys and girls. During puberty, however, values for boys rise, whereas values for girls decrease. In men, these higher values persist to age 40 or 50, decline slowly to age 70, and then decrease rapidly thereafter. In women, the drop in hemoglobin and hematocrit that begins with puberty reverses at about age 50 but never rises to prepubertal levels or to that of men of the same age.

The difference between men and women results partly from menstrual blood loss in women and partly from the effects of androgens in men. Castration of men usually causes hemoglobin and hematocrit to decline to nearly the same levels as those of women. Note that a decline in erythrocytes is experienced by both genders in old age.²¹

More detailed discussions of the RBC and WBC components of the CBC are included in succeeding sections of this chapter. Platelets are discussed in Chapter 2 - Hemostasis and Tests of Hemostatic Functions.

• The components of the CBC and their reference values across the life cycle are shown in Table 1-4.

Because the CBC provides much information about the overall health of the individual, it is an essential component of a complete physical examination, especially when performed on admission to a health-care facility or before surgery. Other indications for a CBC are as follows:

• Suspected hematologic disorder, neoplasm, or immunologic abnormality
• History of hereditary hematologic abnormality
• Suspected infection (local or systemic, acute or chronic)
• Monitoring effects of physical or emotional stress
• Monitoring desired responses to drug therapy and undesired reactions to drugs that may cause blood dyscrasias (Table 1-5)
• Monitoring progression of nonhematologic disorders such as chronic obstructive pulmonary disease, malabsorption syndromes, malignancies, and renal disease

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

A venipuncture is performed and the sample collected in a lavender-topped tube. A capillary sample may be obtained in infants and children, as well as in adults for whom venipuncture may not be feasible.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample (see Appendix I).

• Abnormal range of values: Note and report decreases in individual or entire CBC (pancytopenia) panel. Prepare to administer drugs and treatments, or both, that have been ordered to manage anemia (RBC, hematocrit [Hct], hemoglobin [Hgb], RBC indices), clotting process (platelet), or infectious process (WBC, differential).