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Antistreptolysin O titer

  • Definition

    Antistreptolysin O (ASO) titer is a blood test to measure antibodies against streptolysin O, a substance produced by group A Streptococcus bacteria.

    Alternative Names

    ASO titer; ASLO

    How the test is performed

    Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

    Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

    In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

    The blood is then sent to the laboratory for analysis.

    How to prepare for the test

    You should not eat for 6 hours before the test.

    How the test will feel

    When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

    Why the test is performed

    This test is used to detect prior infection by group A Streptococcus, the bacteria responsible for diseases such as:

    • Bacterial endocarditis
    • Glomerulonephritis
    • Rheumatic fever
    • Scarlet fever
    • Strep throat

    The ASO antibody may be found in the blood weeks or months after the strep infection has gone away.