Background: Family physicians measure serum levels of anti-streptolysin O antibodies (ASO) in the routine evaluation of patients with rheumatic conditions.
Aim: To evaluate the significance of elevated serum ASO titer in hospitalized patients with various clinical conditions.
Patients and methods: We retrieved the names of all patients in whom ASO serum titer was tested in our hospital during two successive years. We chose only those with titers of 1 : 160 or greater (cut-off level < 1 : 80) or with no titer. Their charts were reviewed and the causes for their hospitalization and the reasons for requesting the tests were identified. We also measured the ASO serum titer in 60 healthy individuals.
Results: Six hundred and twenty-five patients were tested for ASO serum levels; 129 patients were negative. In 291 (44%) patients tests were positive at low titers (< 1 : 160). In 205 (33%) the serum titers of ASO were ≥ 1 : 160. We analyzed two groups: those with high ASO titers (≥ 1 : 160) (group 1) and those who were negative for this test (group 2). In group 1, streptococcal cultures were positive only in 14% of the patients with elevated ASO. There was no correlation between ASO serum levels and erythrocyte sedimentation rate, C-reactive protein or rheumatoid factor. In only five individuals (8%) of the healthy cohort, was ASO significantly elevated.
Conclusions: Elevated ASO titers can be found in various clinical conditions other than the typical post-streptococcal associated diseases. In these cases it is not necessarily accompanied by positive culture and does not correlate with inflammatory parameters.