Complete Blood Count Test

Written by:  Leigh A. Zaykoski • Edited by: Leigh A. Zaykoski
Published Nov 22, 2008

The complete blood count test gives doctors a clear picture of how the body is reacting to certain medical conditions and can also help to diagnose some conditions. Learn about how the test is performed and what it reveals.

One of the many ways in which doctors diagnose medical problems is with the use of blood testing. One of the most common blood tests that is performed is the complete blood count, which is simply a test that measures the values of blood components. The complete blood count may be ordered if someone is exhibiting signs and symptoms of anemia or a clotting disorder, or it may be done as a routine procedure during testing prior to a surgical procedure or hospital admission (National Heart Lung and Blood Institute). Learning about all of the blood components tested in a complete blood count test will help you to understand why your doctor has ordered the test and what the results will mean for your health.

Complete Blood Count: Testing Procedure

The complete blood count is a blood test that is performed in a laboratory, using a blood sample from a patient. This sample is obtained through the use of venipuncture, which is when a needle is inserted into a vein so that blood can be collected. The sample is collected in a vacuum tube and sent to the lab for analysis. In the laboratory, technicians analyze the sample to determine the number or quality of specific blood cell components. These values are compared against a normal reference range to determine if they are too high or too low (Lab Tests Online).

Complete Blood Count: Results

The results of the complete blood count test will show the values of the different components of the blood. Levels that are too low or too high can indicate specific problems or that further testing needs to be done to diagnose a medical condition. Red blood cells are one of the blood components analyzed in a complete blood count. If the level of red blood cells in the blood is too high or too low, it can indicate medical conditions such as anemia, bleeding disorders, or dehydration. The white blood cells help the body to fight infection, so abnormal values can indicate infections or cancers within the body. Hemoglobin is an important part of the red blood cells. Hemoglobin carries oxygen, so abnormal levels can indicate the presence of anemia and other blood disorders (National Heart Lung and Blood Institute).

There are other values tested with a complete blood count to provide a complete picture of what is going on in a patient's body. Platelets stick together and help the blood to clot. If a platelet count is too low, it can indicate that the patient has a bleeding disorder where the blood cannot clot properly. If the platelet count is too high, it can indicate that the patient has a clotting disorder where the blood clots too much. Mean corpuscular volume is a measure of the size of the red blood cells. This value is just another tool that helps doctors determine a diagnose or if more testing is needed. Mean platelet volume measures the size of the platelets in the blood. These values can be distorted in the presence of many medical conditions.

Using a complete blood count test is just one way for physicians to determine what is going on and if additional medical tests are needed to make a diagnosis. If your results are abnormal, your physician may recommend additional blood testing or more specific diagnostic testing to eliminate some possibilities and come to a conclusion about what is causing your values to be abnormal. If you are unsure of why these tests are being ordered, ask your physician for an explanation so that you can be an active participant in the management of your health.

Complete Blood Count Reference Materials

National Heart Lung and Blood Institute. Common Blood Tests: Complete Blood Count. Retrieved November 22, 2008 from

Lab Tests Online. "Complete Blood Count." Retrieved November 22, 2008 from

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