ABSTRACT
BACKGROUND: Anti-streptolysin O (ASO) test is usually used to diagnose group A streptococcal infection-related diseases, such as rheumatic fever, reactive arthritis, and various infectious diseases. Despite the recent declining incidence of these diseases, ASO test is still frequently performed as a screening test to diagnose rheumatic diseases. This study re-evaluated the clinical usefulness of ASO test in systemic rheumatic diseases (SRD). METHODS: ASO tests was performed in 825 patients between April and October in 2010. ASO levels were compared between SRD and non-SRD groups of patients. The results of ASO, C-reactive protein (CRP), and rheumatoid factor (RF) were compared among 6 subgroups of SRD: rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis, Behcet disease, Sjogren's syndrome and others. RESULTS: Positive results in ASO test (>200 IU/mL) were observed in 15.3% (126/825) of the patients tested. None of the ASO positive patients was, however, diagnosed with rheumatic fever or reactive arthritis. There were no statistically significant differences in the mean value (P=0.688) or positive rate (P=0.835) of ASO test between SRD and non-SRD groups. Positive rates of ASO test were also not statistically significant different among six subgroups of SRD patients (all P>0.05), whereas those of CRP and RF tests were significantly different. CONCLUSIONS: The usefulness of ASO test is very low for diagnosing SRD, although it is frequently carried out as a screening test. We suggest that ASO test must be performed selectively when diseases from group A streptococcal infection are suspected.