The serum titers of anti-streptolysin O (ASLO) may be of important diagnostic value in patients having a recent streptococcal group A infection, since the sequels of such infections include rheumatic fever, glomerulonephritis and erythema nodosum.
Increased titers of ASLO develop after the second week of infection and reach a peak in 4 to 6 weeks: this peak usually occurs shortly after the onset of rheumatic fever.
ASLO is present in most individuals in low titers since streptococcal infections are common. Therefore, comparison of ASLO titers at (bi-) weekly intervals yields more valuable information than a single determination.