Patients with arthritis will probably have blood tests as part of their initial evaluation and follow-up care. This is because blood is the most easily and safely sampled body tissue, and it contains traces of material from every other part of the body. The most common blood tests used to assist in the diagnosis and management of arthritis include:
Complete blood count (CBC) — The complete blood count is a series of blood tests that provides information about the components of blood including red blood cells, white blood cells, and platelets. Automated machines rapidly count the cell types. The CBC test results can help diagnose diseases and determine their severity.
Under normal conditions, the white blood cell count is between 4,000 to11,000. A high white blood cell count could suggest inflammation, which can be due to rheumatoid arthritis (RA). However, infections, stress, and exercise will temporarily elevate the white blood cell count, too.
A CBC also measures hemoglobin, the iron-containing component of red cells that carries oxygen. The hematocrit is the percent of total blood volume that is made up of red cells. Normal value for males is 39 percent to 51 percent, and 36 percent to 46 percent for females. A lower hematocrit can be caused by a number of factors or conditions including rheumatoid arthritis.
Erythrocyte sedimentation rate (ESR) — The erythrocyte sedimentation rate is a test that involves placing a blood sample in a tube and determining how far the red blood cells settle in one hour. When there is inflammation in the body, it produces proteins in the blood, which make the red cells clump together, causing them to fall faster than the healthy blood cells. Since inflammation can be caused by conditions other than arthritis, the ESR test alone is not diagnostic of arthritis.
Rheumatoid factor (RF) — Rheumatoid factor is an antibody found in many patients with rheumatoid arthritis. It is one of several criteria used in diagnosing RA, as 80 percent of RA patients have RF in their blood. A RF test can be positive in response to other inflammatory or infectious diseases other than RA.
Antinuclear antibody (ANA) — Patients with certain rheumatic diseases, such as lupus, make antibodies that are directed at the nucleus of the body's cells. These antibodies, known as antinuclear antibodies, are detected by viewing the patient's blood serum (clear liquid separated from the blood) under a microscope. A substance containing fluorescent dye that causes the antibodies to bind is then added to the serum. This allows the abnormal antibodies to be seen binding to the nuclei. More than 95 percent of patients with lupus have a positive ANA test. However, patients with other diseases also can have positive ANA test results, and even perfectly healthy people can have positive ANA test results, so other tests must be completed before a definitive diagnosis can be given.
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 8/20/2012…#9845