Rheumatic fever is a systemic connective tissue disorder occurring one to four weeks after an infection by Group A Streptococcus, primarily affecting the heart and joints, and commonly infects children and adolescents. The usual clinical manifestations include carditis, polyarthritis, chorea, erythema marginatum, subcutaneous nodules, joint pain, and fever. Common laboratory tests for this disease include: 1. Complete blood count, often showing mild anemia and a slight increase in white blood cell count. 2. Elevated erythrocyte sedimentation rate. 3. Elevated C-reactive protein. 4. Antistreptolysin-O antibodies often greater than 500 units. 5. Positive throat swab culture. 6. Echocardiogram, which may show vegetations.