Although rheumatoid arthritis (RA) diagnosis typically requires careful observation of symptoms by a physician to discern RA from other types of arthritis and autoimmune conditions, several diagnostic tests are available to supplement the clinical diagnosis. These tests range from general blood tests supporting RA instead of another cause to an RA-specific blood test for rheumatoid factor. When necessary, invasive tests like biopsies or joint fluid testing may supplement blood tests and help exclude other diseases.
Complete Blood Count
Although details of full blood work, called a complete blood count, cannot diagnose RA alone, trends in the blood work results can support a diagnosis of RA. Platelets, cells used for blood clotting, are often increased. The white blood count, which reflects immune system activity, may be increased as well because of the autoimmune nature of RA. In addition, hemoglobin may be low.
C-Reactive Protein
C-reactive protein is useful for first diagnosing RA and for later evaluating the condition. C-reactive protein levels increase in proportion to the amount of inflammation (i.e., swelling) in the body, and RA is associated with swelling around affected joints and tissues. However, C-reactive protein cannot identify the source of swelling, so it is not an RA-specific test.
Rheumatoid Factor
Rheumatoid factor (RF) testing measures the level of an antibody (RF antibody) that occurs in the autoimmune response of RA. RF levels are increased in the majority of people who have RA, but the levels may not be increased in early disease or in a small minority of people who do have RA. Although RF testing is a primary diagnostic tool for RA, the antibody is also present in other autoimmune diseases like lupus and in some types of endocarditis, a heart infection.
References
- "Diagnosis and Management of Rheumatoid Arthritis"; J.A. Rindfleisch and D. Muller; American Family Physician (vol 72) 2005, pp 1037-1047
- University of Virginia Health System: Rheumatoid Arthritis Fact Sheet
- National Institutes of Health: MedlinePlus: Encyclopedia: C-Reactive Protein
- Lab Tests Online: Rheumatoid Factor Test
