The examinations for rheumatic fever include laboratory tests and electrocardiograms, as well as imaging studies. Laboratory tests include indicators of streptococcal infection, commonly using throat swab bacterial cultures, which have a positivity rate of about 20% to 25%. They also include anti-streptolysin O tests, generally considered positive if the titer is above 1:400. Secondly, the tests include those for acute inflammatory response, common markers of which are elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). Electrocardiograms help in detecting various arrhythmias, such as sinus tachycardia and prolonged PR interval. Echocardiography can be used to detect any abnormalities in the mitral valve of the heart.