Analysis of a blood sample can provide important information about rheumatologic conditions, which are marked by inflammation in the joints, muscles, connective tissues, and other structures. The following blood tests are commonly performed to detect or evaluate rheumatologic disorders, including systemic lupus erythematosus (SLE), scleroderma, blood vessel inflammation (vasculitis) and types of arthritis (osteoarthritis, rheumatoid arthritis, psoriatic arthritis, gout and ankylosing spondylitis).
Antibody tests for autoimmune disorders are often necessary. Many rheumatologic conditions—including RA, SLE, and scleroderma—are caused by an abnormal autoimmune response where the body mistakenly releases immune cells to attack healthy tissues.
Complete blood count—a general test that measures the amounts of various blood cells—can provide clues to the presence of inflammation, which tends to increase levels of white blood cells and platelets and decrease the amount of red blood cells.
Blood chemistry screen is another general test that can help to identify problems in the body’s organs, especially the kidneys. Certain types of inflammatory arthritis, including RA, can affect kidney function, as can certain arthritis drugs.
Erythrocyte sedimentation rate (ESR) refers to the rate at which red blood cells, or erythrocytes, settle at the bottom of a test tube to form a sediment. The ESR is increased in many rheumatologic disorders, particularly those associated with vasculitis.
Rheumatoid factor, a type of antibody present in the blood of many individuals with RA, is thought to play a major role in the tissue destruction associated with this disease. About 80% of patients with RA test positive for rheumatoid factor, so this test is considered extremely useful for confirming a diagnosis of this type of arthritis.
Uric acid is the final breakdown product of purines—the building blocks of RNA and DNA. The blood test for this substance is primarily used to detect gout, a form of arthritis that typically affects the joints of the feet and hands. Uric acid levels may also be elevated in some kidney disorders and other conditions that are associated with excessive tissue destruction.
Purpose of the Rheumatology Blood Tests
- To diagnose and monitor rheumatologic and autoimmune disorders
Who Performs It
- A doctor, a nurse, or a lab technician draws the blood sample
- As many as 25% of healthy elderly people have slightly elevated rheumatoid factor levels, and the antibody may also be produced as a result of chronic inflammation unrelated to RA, certain infectious disorders, and certain other diseases.
- In addition to rheumatologic disorders, various other factors may affect ESR values, including age, menstruation and pregnancy, anemia, kidney disease, thyroid disease, certain infections, hormone disorders, cancer, and certain medications and vitamins.
- Uric acid levels may be elevated due to starvation, stress, alcohol abuse, and increased intake of high-purine foods (such as liver, kidney, sweetbreads, and anchovies). Certain medications and vitamins may also alter the test results.
Before the Rheumatology Blood Tests
- Report to your doctor any medications, vitamins, or supplements you are taking. You may be advised to discontinue certain of these agents before the test.
- You must fast for 8 hours before a blood test for uric acid.
What You Experience
- A sample of your blood is drawn from a vein, usually in your arm, and sent to a laboratory for analysis.
Risks and Complications
After the Rheumatology Blood Tests
- Immediately after blood is drawn, pressure is applied (with cotton or gauze) to the puncture site.
- Resume your normal diet and any medications withheld before the test.
- Blood may collect and clot under the skin (hematoma) at the puncture site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.
- Your blood sample is sent to a laboratory for analysis. A physician will review the results for evidence of a rheumatologic disorder.
- If an abnormality is found and your doctor can make a definitive diagnosis, appropriate treatment will begin.
- In many cases, abnormal results on one or more of these blood tests may necessitate additional procedures, such as joint or muscle biopsy, to establish a diagnosis.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media