Minor Criteria
These are arthralgia, fever, prolonged PR interval, raised ESR and C-reactive protein levels. In some cases abdominal pain and epistaxis may occur. Other non specific laboratory findings are leucocytosis and anaemia.
Supportive Evidence
One must always look for supportive evidence for antecedent GAS infection in form of positive throat culture, rising ASO titres, and rapid streptococcal antigen tests. Various antibody tests carried out are anti-streptolysin O, anti-deoxyribonuclease B (ADNaseB), anti-nicotinamide adenosine dinucleotidase (ANA Dase), anti-hyaluronidase and anti-streptokinase.
When two serum samples taken at 2-4 weeks intervals show a two-fold rise, antibody tests are considered positive. The ASO titres of > 250 Todd units in adults and > 333 Todd Units in children are considered positive. The ASO titres may take upto 4-6 months to return to normal, hence by the time chorea or carditis develops after ARF, ASO titres may have returned to normal. In such situation, one may rely on ADNase B levels, as it remains elevated even beyond 6 months after ARF. Diagnosis of ARF is confirmed if 2 major or one major and 2 minor Jones criteria are present along with a supporting evidence of GAS pharyngitis.