Antistreptolysin O (ASO) Test – Reference Range

Generally, an ASO test value below 200 is considered normal. In children under the age of 5, the test value should be less than 100. Results will vary by laboratory.

If your results show that you have an elevated ASO value, you may have a post-streptococcal complication.

If your test is negative and your doctor still thinks you might have a post-streptococcal complication, they may order a second type of antibody test for a follow-up.

If the results of your tests show that your ASO antibodies are increasing, it’s likely that your infection is recent.

Declining antibody levels suggest that your infection is getting better.

ASO antibodies are produced about a week to a month after an initial strep infection.

A small percentage of people with a complication related to a strep infection will not have an elevated ASO. This is especially true with glomerulonephritis that may develop after a skin strep infection.

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