### What is the Antistreptolysin O Titer Test? The Antistreptolysin O (ASO) titer test is a blood test used to detect antibodies produced by your immune system in response to an infection caused by group A streptococcus bacteria. These bacteria can cause infections like strep throat and skin infections. ### When is it Needed? This test is not used to diagnose a current strep infection. Instead, it is used when a doctor suspects that you may have had a previous strep infection that went untreated and is now causing complications. ### What Do the Results Indicate? - **Negative or Low ASO Levels**: You probably haven't had a recent strep infection. - **Elevated ASO Levels**: You likely had a recent strep infection. - **Increasing ASO Levels**: Indicates a recent strep infection. - **Decreasing ASO Levels**: Suggests that the infection may be clearing up. ### Why Might You Need This Test? You may need an ASO titer test if your healthcare provider suspects complications from a previous strep infection, such as: - **Infections**: Untreated strep can spread to other parts of the body, causing infections in the tonsils, sinuses, skin, middle ear, and blood. - **Scarlet Fever**: Common in children aged 5-15, it can cause complications if untreated. - **Rheumatic Fever**: An inflammatory response that can affect the heart, joints, brain, and skin. - **Glomerulonephritis**: A kidney disease that can lead to kidney failure. ### How is the Test Done? A blood sample is drawn from a vein, usually in your hand or arm. You may be asked not to eat for six hours before the test. ### Additional Tests If your healthcare provider suspects a current strep infection, you might need a rapid streptococcal antigen test or a throat culture. For rheumatic fever, other antibody tests like Anti-DNAse B, anti-hyaluronidase, or anti-streptozyme may be needed.