Description of the test
Blood is made up of many different components. A CBC test looks at the size, shape, and numbers of cells in the blood as well as other characteristics of the blood. The test looks at the:
- number of red blood cells
- number of white blood cells
- numbers of white blood cell types
- number of platelets
- volume of red blood cells in the blood (also called hematocrit)
- amount of hemoglobin (carries oxygen to cells)
- size and shape of the cells (abnormal cells may indicate an infection or conditions such as anemia)
- other measurements related to red blood cells
A patient having blood collected for a complete blood count test
How often should this test be performed?
The frequency of this test is determined by your doctor. More frequent testing may be recommended if you have serious conditions such as anemia, malaria, hemophilia, or certain types of cancer.
Why is this test performed?
Doctors often request this test to get a better understanding of a person's overall health. Results from this test may provide valuable clues if the person is experiencing signs of fatigue or sluggishness which is often related to anemia.
The test can also help diagnose certain conditions such as leukemia, bleeding disorders, infection (e.g., bacterial infections, appendicitis, viral infections, malaria), and to evaluate the body's response to certain medications.
Are there any risks and precautions I should know about?
There is very low risk of side effects with this test. Some people experience slight bruising or tenderness where the needle enters the vein.
The test may have a risk of infection (if the area is not properly sterilized before the sample is taken), bleeding from where the needle was inserted, or bruising around the area where the needle was inserted.
People with bleeding disorders or anyone taking medication that reduces the ability of the blood to clot (e.g., warfarin, aspirin, or other anticoagulants) should tell the technician before the samples of blood are taken. These conditions and medications may require special attention at the time of testing.