Contributed by – Healthians Team
What is the ASO titer test?
Whenever you come in contact with harmful bacteria, your body produces antibodies against them to defend itself. An ASO (antistreptolysin O) test basically checks for specific antibodies that the body produces in response to a toxin called streptolysin O. Streptolysin O is produced by group A Streptococcus (GAS) bacteria. So, when you come in contact with this bacteria and develop a strep infection, your body makes antistreptolysin O antibodies to fight the bacteria and the test aims to detect these antibodies.
Who should get an ASO titer Test?
A doctor will usually order an ASO test if he/she suspects strep infection. Following symptoms are usually a sign:
- Fever
- Joint pain and swelling
- Small, painless nodules under the skin
- Skin rash
- inflammation of the heart
- Fatigue
- High blood pressure
- Shortness of breath
However, these symptoms can be due to other illnesses as well. To confirm the diagnosis, the ASO titer test may be performed twice, with samples collected about two weeks apart.
Why is the ASO titer test needed?
Usually, a strep infection can be treated with antibiotics. But, in some cases, no symptoms of the infection appear and it goes undetected which in long term can cause complications, especially in young children. These are known as post-streptococcal complications. With an ASO titer test, the doctor can determine if you had a strep infection by measuring the antibodies in the blood.
Note that ASO levels are not detectable for at least a week after getting infected. Therefore, this test cannot be used to diagnose recent infections. Usually, it is performed when someone has symptoms suggesting complications due to a strep infection.
What does ASO titer test results mean?
The body produces ASO antibodies about a week to a month after first getting infected. These antibodies peaks at about 3 to 5 weeks after the illness and then diminishes but can stay detectable for several months.
Generally, ASO titer normal range for adults is below 200, while for kids under the age of 5, it is below 100. Remember that this range can vary from lab to lab and only a healthcare professional can better understand them.
If the results show elevated ASO levels, then that could mean post-streptococcal complications. Whereas, a negative ASO could mean the patient tested most likely has not had a recent strep infection. But if the doctor still suspects the infection, a second test may be performed to confirm the diagnosis. If the ASO level rises, then that could possibly mean the infection is recent.
How is the ASO titer test done?
The ASO titer is a simple blood test. There is no preparation needed. You would not have to refrain from eating or drinking. Still, if you are on any medications or have any prior medical conditions, be sure to inform your doctor about that.
For the testing, you will have to give your blood sample. It is a simple procedure, usually completed in a few minutes. A trained sample collector will take the blood from a vein in your arm by inserting a needle attached to a tube. Then the sample is sent to a lab for testing.
