Complete blood count (CBC) is a test that measures the size, shape, and number of different types of cells (red blood cell, white blood cell, platelets) in the blood. The different types of white blood cells (e.g., neutrophils, lymphocytes) may also be measured.
A CBC test will also provide other information about the blood, such as the amount of hemoglobin (the protein that carries oxygen in the blood) and hematocrit (the volume of blood that is made up of red blood cells) in the blood.
Your doctor may suggest this test to you for a number of reasons:
- to assess your overall health
- to diagnose medical causes for symptoms such as fatigue, weakness, fever, bruising, or weight loss
- to diagnose medical conditions such as anemia, polycythemia, infection, leukemia, or bleeding disorders
- to monitor progression of medical condition or treatment
Risks and precautions
CBC is usually a straightforward and safe procedure. However, there are some risks of complications or side effects, including:
- excessive bleeding
- fainting or feeling lightheaded
- blood accumulating under the skin
- swollen vein
Before the test
There is no special preparation needed for this test. If other blood tests are also being performed at the same time, you may be given instructions before the test. For example, if your blood sugar or cholesterol is being tested, you may be asked not to eat or drink anything (except water) for up to 12 hours before the test.
Be sure to tell your health care provider if you have a clotting disorder or are taking any medications (e.g., aspirin, warfarin) that can affect your blood-clotting abilities.
If you are taking any prescription or over-the-counter (non-prescription) medications, supplements, or herbal products, make sure you inform your doctor or pharmacist. Ask them whether it is necessary for you to stop taking any of these medications and products before the test. It is also important to tell them if you have allergies to certain medications or have certain medical conditions.