A complete blood count (CBC) is a blood test that measures the different molecules that make up blood and compares them to a scale of normal values. CBCs can diagnose medical conditions, monitor disease progression, or determine an infection. The test requires a blood sample and counts the amount of red blood cells, white blood cells, and platelets. CBCs are compared to a normal range and abnormalities are analyzed by both the lab and a doctor.
A complete blood count (CBC) is a blood test that doctors can use to diagnose certain medical conditions, monitor the progression of a disease, or determine an infection. CBCs measure the different molecules that make up blood and compare them to a scale of normal values for each molecule. The test is done in a doctor’s office, laboratory, or hospital and requires a blood sample, often taken from the arm using a needle. Blood sampling takes very little time, but the results can take several days depending on the laboratory used to conduct the analysis.
Blood is made up of three types of cells: red blood cells, white blood cells, and platelets. A CBC counts the amount of each of these cell types. A machine uses light detectors to analyze a small blood sample and count the number of cells. Cell types are determined by analyzing the structure, components and size of the cells.
A complete blood count usually analyzes all blood components contained in red and white blood cells and platelets. A white blood cell count will not only include a total number of white blood cells, but will also look at the different types of white blood cells, which can be divided into five subsets. Neutrophils are the infection-fighting white blood cells and should make up about half of your white blood cell count. Low levels of neutrophils can make people more susceptible to infections and can indicate the presence of autoimmune diseases. Other types of white blood cells are lymphocytes, basophils, monocytes, and eosinophils.
In a complete blood count, lymphocyte levels may be higher in some types of infections, including viral infections, or may indicate leukemia. Monocytes are usually evaluated when a bacterial infection is suspected. Increased eosinophils may indicate a parasitic infection.
Red blood cells are counted and evaluated for their value of hemoglobin (HGB), which carries oxygen from the lungs to the rest of the body. A lower than normal hemoglobin level can indicate anemia, which can be caused by low iron levels in the blood or by other diseases. Hematocrit (HCV) is measured as a percentage in relation to the total blood volume and is evaluated in a complete blood count to determine internal bleeding, for example, from traumatic injury during an accident or suspected ectopic pregnancy. HCV levels are routinely checked after surgery that has resulted in blood loss.
Platelets are evaluated in terms of size and number. A low platelet count, called thrombocythenia, can cause excessive bleeding when cut, bruising, and heavier menstrual periods. High counts, called thrombocytosis, indicate an increased risk of stroke due to the formation of blood counts. Taking blood thinners often reduces platelet volume, and doctors often order a complete blood count to make sure the platelet count is decreasing without becoming dangerously low.
A complete blood count is compared to a normal range. This range is different in children, and there is some degree of difference between the counts of men and women. Corresponding normal ranges often appear on CBC reports.
Both the lab and a doctor will analyze the complete blood count for anything significantly out of range. In fact, patients may not actually see the CBC lab report. However, patients can request to see the report and ask their doctor to explain any abnormalities.
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