Antistreptolysin O test is diagnostic in

In rheumatic fever, a retrospective diagnosis of streptococcal infection may be established by demonstrating a high level of antibody to the streptococcal toxin. The standard test is Antistreptolysin O titration: ASO titer higher than 200 is indicative of prior streptococcal infection. Usually, high levels are found in acute rheumatic fever but in glomerulonephritis, titers are often low. Reference: Textbook of Microbiology; Anathanarayan and paniker's; 10th edition; Page no: 218