The Rheumatoid Arthritis (RA) serum test measures the presence of specific antibodies, primarily rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP), associated with rheumatoid arthritis. Elevated levels of these antibodies indicate an immune response that may suggest RA, aiding in early diagnosis and management. This test is often combined with other clinical assessments to confirm RA diagnosis and monitor disease progression.