Information provided by the National Institute of Arthritis and Musculoskeletal and Skin Diseases
Diagnosing lupus can be difficult. It may take months or even years for doctors to piece together the symptoms to diagnose this complex disease accurately. Making a correct diagnosis of lupus requires knowledge and awareness on the part of the doctor and good communication on the part of the patient. Giving the doctor a complete, accurate medical history (for example, what health problems you have had and for how long) is critical to the process of diagnosis. This information, along with a physical examination and the results of laboratory tests, helps the doctor consider other diseases that may mimic lupus, or determine if you truly have the disease. Reaching a diagnosis may take time as new symptoms appear.
No single test can determine whether a person has lupus, but several laboratory tests may help the doctor to confirm a diagnosis of lupus or rule out other causes for a person’s symptoms. The most useful tests identify certain autoantibodies often present in the blood of people with lupus. For example, the antinuclear antibody (ANA) test is commonly used to look for autoantibodies that react against components of the nucleus, or “command center,” of the body’s cells. Most people with lupus test positive for ANA; however, there are a number of other causes of a positive ANA besides lupus, including infections and other autoimmune diseases. Occasionally, it is also found in healthy people. The ANA test simply provides another clue for the doctor to consider in making a diagnosis. In addition, there are blood tests for individual types of autoantibodies that are more specific to people with lupus, although not all people with lupus test positive for these and not all people with these antibodies have lupus. These antibodies include anti-DNA, anti-Sm, anti-RNP, anti-Ro (SSA), and anti-La (SSB). The doctor may use these antibody tests to help make a diagnosis of lupus.
Some tests are used less frequently, but may be helpful if the cause of a person’s symptoms remains unclear. The doctor may order a biopsy of the skin or kidneys if those body systems are affected. Some doctors may order a test for anticardiolipin (or antiphospholipid) antibody. The presence of this antibody may indicate increased risk for blood clotting and increased risk for miscarriage in pregnant women with lupus. Again, all these tests merely serve as tools to give the doctor clues and information in making a diagnosis. The doctor will look at the entire picture — medical history, symptoms, and test results — to determine if a person has lupus.
Diagnostic Tools for Lupus
- Medical history
- Complete physical examination
- Laboratory tests: complete blood count (CBC), erythrocyte sedimentation rate (ESR), urinalysis, blood chemistries, complement levels, antinuclear antibody test (ANA), other autoantibody tests (anti-DNA, anti-Sm, anti-RNP, anti-Ro [SSA], anti-La [SSB]), anticardiolipin antibody test
- Skin biopsy
- Kidney biopsy
Other laboratory tests are used to monitor the progress of the disease once it has been diagnosed. A complete blood count, urinalysis, blood chemistries, and the erythrocyte sedimentation rate test (a test to measure inflammation) can provide valuable information. Another common test measures the blood level of a group of substances called complement, which help antibodies fight invaders. A low level of complement could mean the substance is being used up because of an immune response in the body, such as that which occurs during a flare of lupus.
X-rays and other imaging tests can help doctors see the organs affected by SLE.
For more information on lupus and other musculoskeletal health issues, visit www.niams.nih.gov. Join us next month for part 4 of the series on lupus.
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