Document exposure to streptococcal streptolysin O. A marked rise in titer or a persistently elevated titer indicates that a Streptococcus infection or poststreptococcal sequelae are present.
False-positive ASO titers can be caused by increased levels of serum β-lipoprotein produced in liver disease and by contamination of the serum with Bacillus cereus and Pseudomonas sp ASO titers are elevated in 85% of patients with rheumatic fever but may not be elevated in cases involving skin or renal sequelae. For patients suffering from skin or renal involvement, anti-DNase B [test 096289] may be a better choice.
Streptolysin is a hemolysin produced by group A streptococci. In an infected individual streptolysin O acts as a protein antigen, and the patient mounts an antibody response. A rise in antibody level begins about one week after infection and peaks two to three weeks later. In the absence of complications or reinfection, the ASO titer will usually fall to preinfection levels within 6 to 12 months. Both clinical and laboratory findings should be correlated in reaching a diagnosis.