The Anti-Streptolysin O (ASO) Titer – Quantitative test measures the concentration of antibodies against streptolysin O, a toxin produced by Streptococcus bacteria. Elevated ASO titers indicate a recent streptococcal infection, such as strep throat or skin infections, and can help diagnose complications like rheumatic fever or glomerulonephritis. The quantitative aspect of the test provides a precise measurement of antibody levels, which can be used to monitor the progression of the infection or response to treatment. A blood sample is required for this test.