Definition This test detects an antibody known as ASO, or anti-streptolysin O. This antibody appears when a person has certain bacteria in the blood. The bacteria are Group A streptococcus, which make an enzyme called streptolysin O. This enzyme destroys red blood cells.
Who is a candidate for the test? This test can be used to:
How is the test performed? To do the test, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or tourniquet, is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into the vein chosen and the tourniquet is removed. Blood flows from the vein through the needle. It is collected in a syringe or vial for testing in the laboratory. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
What is involved in preparation for the test? A person should request specific instructions from his or her doctor.
What do the test results mean? Test results report the number of international units of antibodies per litre of blood. In a person over 15 years of age, ASO antibody levels are normally less than 360 international units per litre.
Higher-than-normal levels of ASO antibodies may indicate:
active streptococcal infection
bacterial endocarditis, an inflammation in the lining of the heart
post-streptococcal glomerulonephritis, an infection in the kidney
rheumatic fever, a disease that may affect the heart and kidneys
scarlet fever, an infection involving the throat and tongue that causes fever, rash, and rapid pulse
Author: David T. Moran, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 6/06/2005 Contributors Potential conflict of interest information for reviewers available on request
