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

ASO titer; ASLO

A blood sample is needed. For information on how this is done, see: Venipuncture

You should not eat for 6 hours before the test.

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.

This test is done if you have symptoms of a previous infection by group A Streptococcus. Some illnesses caused by this bacteria are:

• Bacterial endocarditis
• Glomerulonephritis, a kidney problem
• Rheumatic fever , which can affect the heart, joints, or bones
• Scarlet fever
• Strep throat

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

A negative test result means you have likely not had a recent strep infection. The healthcare provider may repeat the test again in 2 - 4 weeks. Sometimes a test that was first negative will come back positive.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

An abnormal or positive test means you recently had a strep infection, even if you had no symptoms. The ASO test may stay positive (sometimes called detectable) for 2 to 4 months afterward you are first infected.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

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