Complete Blood Count (CBC), with Differential
A complete blood count (CBC) is a laboratory test that measures several basic parameters of human blood including the red blood cell counts (erythrocytes), white blood cell counts (leukocytes) and platelets (thrombocytes). A CBC with differential is often ordered to determine a patients general health status. These values help medical professionals diagnose certain diseases and
conditions in the human body. This test is frequently ordered in
addition to other basic lab tests for routine physical exams.
Specific Tests In A Complete Blood Count
- White blood cell (WBC) count
- White blood cell differential
- Red blood cell (RBC) count
- Platelet count
- Mean corpuscular volume (MCV)
- Mean corpuscular hemoglobin (MCH)
- Mean corpuscular hemoglobin concentration (MCHC)
- Red cell distribution width (RDW)
Typically, red blood cell counts are analyzed to see if counts are normal, high, or low. Hemoglobin levels measure how much hemoglobin (the vital component in a blood cell) is in the blood while hematocrit levels measure the concentration of hemoglobin against total blood volume. Low amounts may indicate a loss of blood from a variety of reasons. There could be low counts from acute bleeding or a chronic cause such as poor nutrition. Other red blood cell counts are also measured as a useful metric to screen or confirm diseases.
Mean corpuscular volume measures the average size of red blood cells; the average size can help determine if chronic anemia (low blood levels) is present. A red blood cell distribution width measures the variation of size between blood cells. This measure is helpful in determining if blood is being formed properly and quickly enough by bone marrow. A high value may indicate a more serious process like leukemia while a low value may indicate a problem with blood formation in bone marrow, as seen for example in aplastic anemia.
White blood cell (WBC) counts measure the amount of white blood cells, which constitute the body's immune response towards disease and illnesses. A high WBC level can indicate several things, from infection to stress, or even cancer. A low WBC level may indicate a problem with the bone marrow or some immunosuppressive disease such as HIV. A standard CBC measures only the amount of white blood cells in the body while a CBC with differential gives a breakdown of the types of white blood cells in a blood sample.
When a differential is obtained, the breakdown of the five major white blood cell types is analyzed: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. A healthcare provider can then use the differential breakdown to help determine what disease processes may be present.
Platelet counts measure the amount of platelets in the body, which are the body's cellular response to clot off areas of active bleeding. High or low levels may be able to help narrow down a cause for prolonged bleeding or a propensity for a person to have blood clots spontaneously. In addition, mean platelet volume is measured to help look for the presence of platelet-destructive diseases.
A CBC is considered part of the standard set of lab tests ordered for routine examinations, including a basic metabolic panel, urine analysis, and lipid panel, but a CBC is also commonly ordered to detect or measure the progression of diseases. Reasons for ordering a CBC are numerous. For instance, a CBC is often ordered in someone feeling chronic fatigue in order to rule out anemia. When a person has a condition that may cause bleeding, like diverticulitis or colon cancer, a CBC is one of the first tests ordered. Keep in mind that in many cases, slight or moderate elevations or lowering of CBC values may be normal within a proper clinical context. No fasting is required for a proper CBC to be obtained.