Anti-Streptolysin O (ASO) Antibody, Titration

What Is This Test Used For?

Doctors use ASO testing primarily to diagnose **Group A Streptococcus (GAS) infections**, such as strep throat, scarlet fever, or rheumatic fever. It can also help determine if you’ve had a recent strep infection, even if symptoms have cleared. ASO levels rise after infection and may stay elevated for months, so it’s useful for tracking long-term exposure or recurrence.

How Is the Sample Collected?

A blood sample is drawn from a vein in your arm by a healthcare professional. You may feel a brief pinch, but it usually doesn’t cause discomfort. The blood is sent to a lab for testing.

What Does a High or Low ASO Level Mean?

A **high ASO level** suggests you’ve had a recent or past GAS infection. Very high levels may indicate rheumatic fever or other complications. A **low or normal ASO level** means either you haven’t been infected recently or the infection has cleared. Note that ASO testing isn’t definitive for active strep throat—other tests (like rapid strep swabs) may be needed for immediate diagnosis.

How Long Does It Take to Get Results?

Results are typically available within **1–3 business days**, depending on lab processing times. Your doctor will discuss the meaning of your results in relation to your symptoms and medical history.