Serum or Plasma Immunoassay for Anti-Streptococcal Antibodies (Group A Streptococcus)

This test checks for group A strep bacteria (Streptococcus pyogenes), the germ that most often causes strep throat. It helps your healthcare provider find out whether your sore throat is caused by a bacterial infection that needs treatment or by a virus that will usually get better on its own.

The test detects specific antibodies (immunoglobulins) your immune system creates to fight Group A Streptococcus bacteria. These antibodies appear in your blood after infection and can linger for months or years. The presence of these antibodies suggests prior exposure to the bacteria.

Your provider may order this test if you have a sore throat along with symptoms such as fever, swollen glands in your neck, pain when swallowing, or white patches on your tonsils. Knowing whether strep bacteria are present helps your provider decide whether antibiotics are needed, since antibiotics work against strep throat but not against viral sore throats.

Your healthcare provider may order this test if you have symptoms of a strep infection (e.g., sore throat, fever, red rash) or if you’ve been exposed to someone with a strep infection. It can also help confirm a diagnosis when other tests (like rapid strep swabs) are inconclusive.

The test uses a sample taken from the back of your throat. A soft cotton swab is rubbed gently over your tonsils and the area around them to collect material. That swab is then checked for group A strep bacteria, either with a rapid test that can give results within minutes or with a throat culture that is sent to a laboratory.

A blood sample is taken from a vein in your arm. The blood is sent to a lab where it’s analyzed using an immunoassay method to identify the presence of antibodies against Group A Streptococcus. This method detects the antibodies without measuring the bacteria directly.

No special preparation is usually needed for this test. You can eat and drink as usual and keep taking your regular medicines unless your provider tells you otherwise. Try to avoid using mouthwash or throat sprays right before the appointment, and let the staff know if you have a strong gag reflex or trouble opening your mouth so they can make the swab as comfortable as possible.

No special preparation is needed. You may have a slight bruise or discomfort at the injection site, but this usually fades quickly. Avoid alcohol for 24 hours before the test if possible, as it may affect lab results.