Rheumatoid arthritis laboratory tests
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Laboratory tests
Blood tests
- Rheumatoid factor:
- When RA is being clinically suspected, immunological studies are required, such as rheumatoid factor (RF, a specific antibody).[1]
- A negative RF does not rule out RA; rather, the arthritis is called seronegative
- During the first year of illness, rheumatoid factor is frequently negative. 80% of patients eventually convert to seropositive status. RF is also seen in other illnesses, like Sjögren's syndrome, and in approximately 10% of the healthy population, therefore the test is not very specific.
- Anti-citrullinated protein:
- Because of this low specificity, a new serological test has been developed in recent years, which tests for the presence of so called anti-citrullinated protein antibodies (ACPA).
- Like RF, this test can detect approximately 80% of all RA patients, but is rarely positive in non-RA patients, giving it a specificity of around 98%. In addition, ACP antibodies can be often detected in early stages of the disease, or even before disease onset. Currently, the most common test for ACP antibodies is the anti-CCP (cyclic citrullinated peptide) test.[2]
- ESR and CRP:
- Also, several other blood tests are usually done to allow for other causes of arthritis, such as lupus erythematosus. The erythrocyte sedimentation rate (ESR), C-reactive protein,[3]
full blood count, renal function, liver enzymes and other immunological tests (e.g. antinuclear antibody/ANA)[4] are all performed at this stage. Ferritin can reveal hemochromatosis, which can mimic RA.
References
- ↑ "Rheumatoid Factor". Lab Tests Online. American Association for Clinical Chemistry. September 30, 2006. Retrieved 2006-10-28.
- ↑ "CCP (Cyclic Citrullinated Peptide antibody)". Lab Tests Online. American Association for Clinical Chemistry. January 15, 2005. Retrieved 2006-10-28.
- ↑ "C-Reactive Protein". Lab Tests Online. American Association for Clinical Chemistry. September 3, 2004. Retrieved 2006-10-28.
- ↑ "ANA (Antinuclear Antibody)". Lab Tests Online. American Association for Clinical Chemistry. December 13, 2004. Retrieved 2006-10-28.