complete blood count

complete blood count (CBC), laboratory test that measures the number and characteristics of multiple different blood components. A complete blood count (CBC) test provides insight into an individual’s overall health. Such tests also are often used to help detect or diagnose a wide range of diseases and disorders, including anemia, infection, and various cancers.

A CBC quantifies red blood cells (erythrocytes), white blood cells (leukocytes), platelets, hemoglobin, and hematocrit (the portion of blood consisting of red blood cells). A CBC also can be used to provide measures of red cell indices, such as the average size of red cells and the amount of hemoglobin they contain, and to quantify reticulocytes (the number of immature red blood cells present). A test known as a white blood cell differential is sometimes carried out alongside a CBC. The differential measures the percentage of each type of white blood cell per 100 white cells counted.

CBC is carried out by first collecting a blood sample from the patient. The sample is then passed through an automated hematology analyzer, a machine designed to detect changes in electrical resistance of particles that are suspended in an electrolyte solution. As each cell travels through a narrow aperture in the machine, its displaces an electrolyte, producing a fleeting change in electrical resistance. The analyzer measures this change and correlates it to cell number and size.

CBC readings vary with age, sex, physiological state, and general health, but typically, the blood of a healthy adult male contains about 4.3–5.9 million red cells per cubic millimeter, while that of a female contains about 3.5–5.5 million red cells per equivalent volume. A typical white blood cell count is 4.5–11.0 thousand cells per cubic millimeter. The white cells of a healthy adult are between 40 and 60 percent neutrophils, between 20 and 40 percent lymphocytes, and between 2 and 8 percent monocytes, with small percentages of eosinophils and basophils.

Atypical CBC readings are indicative of health conditions. A decrease in the number of red blood cells, for example, is usually associated with anemia, while an increase or decrease in the number of white blood cells can occur with infections, inflammatory conditions, or leukemia.