Anti DNA as -B is used for diagnosis of -

Ans. is 'b' i.e., Streptococcus Evidence of antecedent group 'A' streptococcal infectiono Positive throat cultures or rapid streptococcal antigen tests for group A streptococcoci are less reliable for antecedent infection capable of producing rheumatic fever because they do not distinguish between recent infection and chronic pharyngeal carriage (as many people are carrier of this bacteria),o Antibody tests are the most reliable laboratory evidence of antecedent streptococcal infection capable of producing acute rheumatic fever. The onset of clinical manifestations of acute rheumatic fever coincides with the peak of the streptococcal antibody response.o The antibodies used commonly for serological tests are antistreptolysin O (ASO), antideoxyribonuclease f Anti- DNAse) and antihyaluronidase.o ASO titre is well standardized and therefore is most widely used test. It has following features.Elevated in 80% of patients with acute rheumatic fever (So, 20% patients do not show elevated titre) - Sensitivity is 80%.It is elevated in 20% of normal individuals particularly in healthy school children of elementary school age (20% false positive).ASO titers of at least 333 Todd units in children and 250 Todd units in adults are considered elevated.It is included in minor criteria of jones criteria (not in major criteria).o Anti DNAse B titers of240 Todd units or greater in children and 1200 Todd units or greater in adults are considered elevated.o If three antibody tests (ASO, anti-DNAse and anti-hyaluronidase) are used simultaneously, a titer for at least one antibody test is elevated in 95% of cases - Sensitivity of combined three antibody tests is 95%.