Complete Blood Count (CBC)

A complete blood count (CBC) is the most commonly performed lab test in the U.S. and is used to analyze red blood cells (RBCs), white blood cells (WBCs), and platelets. Many people with systemic lupus have abnormal CBCs. White blood cell counts can be low (leukopenia) due to lupus, immunosuppressive therapy, or the presence of a virus. High WBC counts may signal infection but also occur when individuals are on corticosteroids such as prednisone. Usually, your doctor will request that your white blood cell differential is also assessed as a part of your CBC. There are five types of white blood cells: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Each group of white blood cells plays a different role in the immune response. The white blood cell differential will measure whether these cells are present in your body in normal proportions, revealing information about certain deficiencies in your immune system. For example, both lupus and prednisone tend to lower an individual’s lymphocyte count.

In addition, a CBC will measure whether an individual’s platelet level is low (thrombocytopenia), indicating that either the bone marrow is not making enough platelets or that antibodies are attacking them. A complete blood count will also assess whether red blood cell counts are low. Low red blood cell counts can indicate anemia caused by bleeding, medications, “chronic disease,” autoimmune hemolytic anemia (breakdown of RBCs due to auto-antibodies), or a vitamin deficiency. About 40% of people with lupus will be anemic at some time during the course of the disease. The most common types of anemia are iron-deficiency anemia and anemia of “chronic disease.”


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  • Wallace, Daniel J. The Lupus Book: A Guide for Patients and Their Families. 1st ed. New York: Oxford University Press, 1995. 61.