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Tests and diagnosis
By Mayo Clinic staffReactive arthritis can go undiagnosed for a long time because your signs and symptoms may be mild. While there is no single test that will confirm a diagnosis of reactive arthritis, the results of a variety of tests can be taken together to rule out other conditions that may be causing your signs and symptoms.
Blood tests
Samples of your blood can reveal:
- Infections. Sometimes, the triggering bacteria are still evident in your blood. But in many cases, your reactive arthritis symptoms begin long after you've recovered from the infection.
- Inflammation. Your doctor may check a blood test to see if you have an elevated sedimentation rate — which is the speed at which your red blood cells settle to the bottom of a tube. An elevated rate can indicate inflammation. People with reactive arthritis often have an elevated sedimentation rate.
- Evidence of other problems. Rheumatoid factor is an antibody often found in the blood of people with rheumatoid arthritis. Anti-nuclear antibodies are proteins that are generally found in people who have connective tissue or autoimmune disorders. If you have reactive arthritis, you'll probably test negative on both of these tests.
- Genetic markers. The inherited HLA-B27 antigen increases your risk of reactive arthritis. Reactive arthritis can also occur in people without HLA-B27.
Joint fluid tests
Your doctor may use a needle to withdraw a sample of fluid from within an affected joint. This fluid will be tested for:
- Infections. Even though reactive arthritis is triggered by an infection in another part of your body, this infection doesn't affect your joints. If an infection is found in your joint fluid, you may have septic arthritis, which can result in severe joint damage.
- Crystals. If uric acid crystals are found in your joint fluid, you may have gout. This very painful type of arthritis often affects the big toe.
Tests of other body fluids
Your doctor may also check for infections in your:
- Urine
- Stool
- Genital secretions
- Throat mucus
Imaging tests
X-rays of your joints can indicate whether you have any of the characteristic signs of reactive arthritis, including soft tissue swelling, calcium deposits where tendons attach to bones and cartilage damage. X-rays can also rule out other types of arthritis.
- Reiter's syndrome and reactive arthritis. In: Noble J, et al. Textbook of Primary Care Medicine. 3rd ed. St. Louis, Mo.: Mosby; 2001. http://www.mdconsult.com/das/book/body/114024667-3/784198713/959/880.html#4-u1.0-B0-323-00828-3..50142-4--cesec10_4248. Accessed Dec. 17, 2008.
- Yu DT. Reactive arthritis (formerly Reiter syndrome). http://www.uptodate.com/home/index.html. Accessed Dec. 17, 2008.
- Questions and answers about reactive arthritis. National Institute of Arthritis and Musculoskeletal and Skin Diseases. http://www.niams.nih.gov/Health_Info/Reactive_Arthritis/default.asp. Accessed Dec. 17, 2008.
- Leirisalo-Repo M, et al. Reactive arthritis. In: Firestein GS, et al. Kelley's Textbook of Rheumatology. 8th ed. Philadelphia, Pa.: W.B. Saunders; 2008. http://www.mdconsult.com/das/book/body/114235812-3/784844632/1807/526.html#4-u1.0-B978-1-4160-3285-4..10071-3--s0160_2594. Accessed Dec. 19, 2008.
- Septic arthritis. American Association for Clinical Chemistry. http://www.labtestsonline.org/understanding/conditions/septic.html. Accessed Dec. 19, 2008.
- Questions and answers about gout. National Institute of Arthritis and Musculoskeletal and Skin Diseases. http://www.niams.nih.gov/Health_Info/Gout/default.asp. Dec. 19, 2008.
