Serum or Plasma Immunoassay for Anti-Streptolysin O Antibodies (ASO)

What Does This Test Measure?

The ASO test detects antibodies (specifically anti-streptolysin O) your body creates when exposed to certain bacterial toxins produced by Group A Streptococcus. These antibodies are a marker of past infection and can indicate whether you had strep throat or scarlet fever.

Why Might You Need This Test?

Your healthcare provider may order this test if you have symptoms like sore throat, fever, rash, or joint pain that suggest strep infection, especially if antibiotics didn’t fully resolve symptoms. It can also help confirm a diagnosis in cases where other tests are inconclusive.

How Is the Test Performed?

A blood sample is taken from a vein in your arm. The blood is then processed to separate serum or plasma, which is tested for ASO antibodies using an immunoassay method. This method detects the presence of specific antibodies against streptococcal toxins.

What Are Possible Results?

Results are qualitative (positive or negative) and indicate whether your immune system has mounted an antibody response to Group A Streptococcus. A positive result suggests past infection, while a negative result means no detectable antibodies are present.