Understand the Antistreptolysin O Titer and Its Significance

Whenever your body is exposed to harmful bacteria, it naturally produces antibodies to defend itself. In the case of a Group A Streptococcus (GAS) infection, the bacteria release a toxin known as Streptolysin O and in response, your immune system produces a specific antibody called Antistreptolysin O (ASO) to neutralise it. The ASO titer is a blood test that measures the level of these antibodies in your bloodstream. Read on to know more about this test.

What is Antistreptolysin O Titer?

The antistreptolysin O (ASO) titer test is a diagnostic procedure (blood test) that measures the level of antibodies against streptolysin O, a toxin produced by Group A Streptococcus (GAS) bacteria. It is to determine if the person have had a recent Streptococcus infection.

Purpose of Antistreptolysin O Titer

An ASO titer test is not used to diagnose an active strep infection, as your body typically needs one to three weeks after infection to produce detectable levels of antibodies. It is to help doctors determine whether a past streptococcal infection has led to complications like rheumatic fever, post-streptococcal glomerulonephritis or scarlet fever. This is especially relevant if you are experiencing unexplained joint pain, kidney issues or heart inflammation, which can occur weeks after an untreated strep infection.

How the Test Works?

The test measures the amount (titer) of ASO antibodies in your blood. A higher ASO level may indicate a recent streptococcal infection, even if you didn’t experience obvious symptoms at the time. This helps doctors diagnose complications like rheumatic fever or glomerulonephritis, especially when symptoms appear weeks after the original infection. In case of any complications, it is smart that you buy health insurance well in advance. This way, you won’t have to worry about high medical costs and get the appropriate treatment.

The normal values of test is:

- Adults: Less than 200 units/mL

- Children (aged below 5 years): Less than 100-150 units/mL

How Is an Antistreptolysin O Titer Test Done?

Like all normal blood tests, the ASO titer is also done by drawing a blood sample from your vein (usually from a vein in your arm).

Here are some tips to follow before this test:

• You may have to fast for six hours before the test. Please confirm the details with your doctor for your test to show proper results.

• Let your doctor know of all your current medications. They might ask you to stop a few medications (like blood thinners, steroids, antibiotics, etc.) for a couple of days before the test so that they don’t interfere with your test results.

Get this test done after two weeks to know if the antibody production in your body has increased or decreased.

What are Some Other Tests You May Need?

To confirm the presence of a recent or ongoing streptococcal infection and decide on the appropriate treatment, your doctor may order additional tests along with the ASO titer. These may include:

• Rapid antigen detection test (RADT) or throat culture to detect an active strep throat infection.

• Blood culture to check if the bacteria have spread to the bloodstream.

• Tissue culture to identify infections in deeper tissues.

• Sputum culture to examine mucus from the lungs in cases of respiratory symptoms.

• Anti-DNase B

• Anti-hyaluronidase

• Anti-streptozyme

These tests provide a more comprehensive understanding of your immune response and help diagnose complications like rheumatic fever, glomerulonephritis or other post-streptococcal conditions that may not be captured by the ASO titer alone.