The antistreptolysin O (ASO) titer test is a blood test that checks for a strep infection. When you come into contact with harmful bacteria, your body produces antibodies to defend itself against these bacteria. Your body produces antibodies specific to the bacteria they fight. The ASO titer test measures antibodies produced by your body in response to a toxin known as streptolysin O. Streptolysin O is a toxin produced by group A Streptococcus (GAS) bacteria. Your body makes the antistreptolysin O antibodies when you have a strep infection caused by GAS bacteria. Usually, when you have a strep infection like strep throat, you receive antibiotics that kill the strep bacteria. But some people don’t have any symptoms during a strep infection and may not know they need treatment. When this happens, an untreated infection can lead to future complications. These complications are known as post-streptococcal complications. The ASO titer test can help your doctor determine if you recently had a strep infection by measuring the presence of antistreptolysin antibodies in your blood.
Why do I need an ASO titer test?
Your doctor will order the ASO titer test if you have symptoms of post-streptococcal complications. Some of the common complications of strep include:
- bacterial endocarditis
- rheumatic fever
The antistreptolysin antibodies peak in your system between three to eight weeks after a strep infection. Levels can remain high for several months. Your doctor can determine if your symptoms are due to a post-streptococcal complication by checking your antibody levels.