The rheumatoid factor (RF) test is used to detect RF antibodies in the blood, which can attack healthy cells and lead to autoimmune conditions. It is primarily used to diagnose rheumatoid arthritis but can also help identify other conditions like Sjögren syndrome, lupus, and certain cancers. Symptoms prompting an RF test include joint pain, swelling, fatigue, and unexplained weight loss. The test involves drawing a small blood sample, and results can indicate the presence of autoimmune diseases or infections, requiring further diagnostic tests if positive. Despite its usefulness, a negative result does not entirely rule out the presence of rheumatoid arthritis or related conditions.

The RF test detects antibodies in the blood that sometimes mistakenly attack healthy cells, leading to autoimmune conditions, and is commonly used to diagnose rheumatoid arthritis, Sjögren syndrome, lupus, and certain cancers.

Healthcare providers may recommend the test if a patient exhibits symptoms such as joint pain, swelling, fatigue, low fever, and unexplained weight loss, which are common indicators of rheumatoid arthritis.

The RF test involves a simple blood draw, typically from a vein in the arm, with results available in a few hours to days, and does not require special preparation, though checking with a healthcare provider about other test requirements is advised.

Results are reported in international units per milliliter or as a titer, with normal ranges usually below 15 IU/mL or a titer of 1 to 80, and a positive result indicates higher RF levels, suggesting possible autoimmune disease or infection.

A positive RF test necessitates further testing, such as C-reactive protein, erythrocyte sedimentation rate, anticyclic citrullinated peptide antibody, and antinuclear antibody tests, to confirm the underlying condition.

Despite a negative result, rheumatoid arthritis or other conditions can't be completely ruled out, as some patients with RA may not have elevated RF levels, necessitating additional testing if symptoms persist.

At-home RF tests are available, allowing patients to mail a blood sample to a laboratory, but results should be shared with a healthcare provider for further interpretation and diagnosis.