Laboratory confirmation of a diagnosis of rheumatic fever can be achieved by

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The most commonly used laboratory test for rheumatic fever is the anti-streptolysin O (ASO) titre, which measures the level of antibodies against streptococcal antigens. Elevated ASO titres are indicative of a recent streptococcal infection, which is a major risk factor for developing rheumatic fever. The other options listed are not commonly used for diagnosing rheumatic fever. Blood cultures may be positive for Streptococcus pyogenes, but this is not specific to rheumatic fever, as this bacterium can also cause other types of infections. Culture of joint fluid could help diagnose septic arthritis, but rheumatic fever is not typically associated with joint infections. Toxin identification is not a useful diagnostic test for rheumatic fever, as the underlying mechanism for disease development is thought to be an autoimmune reaction triggered by a preceding streptococcal infection. X-ray of the heart may be used to detect complications of rheumatic heart disease, but it is not used to diagnose rheumatic fever.

Laboratory Confirmation of a Diagnosis of Rheumatic Fever Can Be