The key difference between rheumatic fever and rheumatoid arthritis primarily lies in the fact that patients with rheumatic fever, besides exhibiting symptoms such as joint pain, also develop cardiac and dermatological manifestations. Patients with rheumatic fever may experience mitral stenosis and symptoms like erythema on the skin. Moreover, the examination of antibodies in rheumatic fever patients mainly shows an elevation in anti-streptolysin O antibody. In contrast, patients with rheumatoid arthritis typically display elevated rheumatoid factor, anti-CCP antibodies, and anti-AKA antibodies, and they seldom have skin or cardiac manifestations. Therefore, to differentiate rheumatic fever from rheumatoid arthritis, one can test for anti-streptolysin O and rheumatoid factor, and further conduct an echocardiogram to determine any cardiac involvement.