Which laboratory test is commonly checked in evaluating rheumatoid arthritis?

• A. ANA
• B. RF
• C. Lyme titer
• D. ESR

Answer: (B)

Rheumatoid factor testing is commonly checked when evaluating rheumatoid arthritis because it helps support the diagnosis in the right clinical context. RF is an autoantibody (often an IgM antibody against the Fc portion of IgG) that is present in a large proportion of people with RA, especially as disease becomes established. Its presence adds diagnostic weight when a patient has inflammatory symmetric polyarthritis and morning stiffness, though it’s important to remember RF is not exclusive to RA and can be seen in other autoimmune conditions and in some healthy older adults. Therefore, RF is a useful, RA-focused test to help confirm the diagnosis alongside clinical findings and, when available, more specific tests like anti-CCP antibodies. In contrast, ANA is more indicative of other autoimmune diseases such as lupus, Lyme titer is used when Lyme disease is a concern, and ESR is a non-specific marker of inflammation useful for monitoring activity but not specific to RA.