A complete blood count (CBC) is a measurement of the components of the blood. This test can help your doctor both diagnose disease and monitor the safety of any treatments administered for a disease. The CBC is also called a blood count, a hemogram, or a CBC with differential.
While many other blood tests measure the amount of a particular drug, chemical, or protein in your blood, the CBC checks the blood cells themselves. It measures the numbers of different types of blood cells as well as their sizes, shapes, color, and other characteristics. Abnormal results in the CBC can reflect problems with the amount of fluid in your body (such as dehydration) or loss of blood. This test can also give an indication of the amounts of iron and some vitamins in your body. It can show abnormalities in the production, life span, and destruction of blood cells. Finally, the CBC can highlight acute or chronic infection, allergies, and problems with clotting.
Having a CBC will take just a few minutes of your time. No special preparation or fasting before the test is necessary. A CBC utilizes a small sample of blood that is usually drawn from a vein in your arm or the back of your hand. The test carries no risk of getting AIDS, hepatitis, or any other bloodborne disease. The blood sample is sent to the lab, where automated machines rapidly count the cell types.
Some of the constituents of the blood that are measured in the CBC include white blood cells (WBC), red blood cells (RBC), and platelets (PLT).
White Blood Cell Count
White blood cells are part of your immune system and help the body fight off infections. Normal values for the WBC count range between 4000 and 10,000 cells per cubic milliliter (cmm). A high WBC count could suggest inflammation, which might be due to RA. However, infections, stress, exercise, and medications such as steroids may also temporarily elevate the WBC count. A low WBC count may result from certain blood diseases, bone marrow failure, and some autoimmune diseases. Some of the medications used to treat RA can lead to low WBC counts, especially the disease-modifying antirheumatic drugs (DMARDs).
Red Blood Cell Count
Red blood cells carry oxygen from the lungs to the rest of the body. They contain hemoglobin, a protein that contains iron and gives blood its red color. Normal values for the RBC count range from 4.2 million to 5.9 million cmm (sometimes expressed simply as 4.2-5.9). Low RBC counts (also called anemia) can have multiple causes in a person with RA:
- RA itself
- A poor diet that includes low amounts of iron and protein
- Bleeding caused by aspirin or nonsteroidal anti-inflammatory drugs such as naproxen or ibuprofen
Platelet Count
Platelets (also called thrombocytes) are not actually blood cells, but rather are fragments of large blood-forming cells. These fragments are essential for normal blood clotting. The normal values for the PLT test vary between laboratories but are usually in the range of 150,000 to 400,000 cmm (sometimes expressed simply as 150-400). An increase in platelet count can be seen with RA, some blood diseases, and some cancers. Low platelet counts may be seen in certain blood diseases and infections, and as the result of certain medications.
Your physician may check your CBC many times each year, depending on the activity of your disease, your symptoms, and the types of medications you are taking.