Antistreptolysin O titer
Alternative Names: ASO titer; ASLO
Antistreptolysin O (ASO) titer is a blood test to measure antibodies against streptolysin O, a substance produced by group A Streptococcus bacteria.
Why is the Test Performed?
This test is used to detect prior infection by group A Streptococcus, the bacteria responsible for diseases such as:
The ASO antibody may be found in the blood weeks or months after the strep infection has gone away.
How is the Test 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.
Preparation for the Test
You should not eat for 6 hours before the test.
How will the Test 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.
Antistreptolysin O titer Risks
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)
Normal Results for Antistreptolysin O titer
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
Abnormal results may be due to:
- Active streptococcal infection
- Bacterial endocarditis
- Post-streptococcal glomerulonephritis
- Rheumatic fever
- Scarlet fever
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Reviewed By: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
Copyright 2011 A.D.A.M., Inc.
