ABSTRACT
The anti-streptolysin O (ASO) test, which depends upon age and geographic location, is used to provide evidence for antecedent streptococcal infection in patients suspected of having rheumatic fever. Reference values of ASO have not previonsly been determined by nephelometric assay for laboratory use at Siriraj Hospital. A total of 402 serum specimens were collected from healthy adults aged between 16 and 63 years in Siriraj Hospital. They consisted of 235 blood donors, 150 subjects who were going to study aboard and 17 dentists. ASO concentrations from 5 groups according to five age ranges were compared and it was found that two age ranges which were 25 years old and younger and 26 years and older were appropriate to determine reference values. The reference values of ASO for these two age ranges, with 90% confidence intervals, were 486 (401-673) IU/ml and 385 (362-500) IU/ml, respectively.