Antistreptolysin O titer
Antistreptolysin O (ASO) titer is a blood test to measure antibodies against streptolysin O, a substance produced by group A Streptococcus bacteria. Antibodies are proteins our bodies produce when they detect harmful substances, such as bacteria.
ASO titer; ASLO
How the Test is Performed
A blood sample is needed.
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 where the needle was inserted.
Why the Test is Performed
This test is done if you have symptoms of a previous infection by group A Streptococcus. Some illnesses caused by this bacteria are:
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 likely have not had a recent strep infection. Your doctor may repeat the test in 2 to 4 weeks. Sometimes, a test that was negative the first time will be positive (meaning it detects ASO antibodies) when it is done again..
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
An abnormal or positive test result 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 after you were first infected.
Veins and arteries vary in size from person to person, and from one side of the body to the other. Because of this, it may be harder to get a blood sample from some people than it is from others.
Other risks associated with having blood drawn are slight, but may include:
- Excessive bleeding where the needle is inserted
- Fainting or feeling light-headed
- Hematoma (blood buildup under the skin)
- Infection (a slight risk any time the skin is broken)
Bisno AL. Nonsuppurative poststreptococcal sequelae: Rheumatic fever and glomerulonephritis. In: Mandell GL, Bennett JE, Dolin R, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2009:chap 199.
Bisno AL, Stevens DL. Streptococcus pyogenes. In: Mandell GL, Bennett JE, Dolin R, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2009:chap 198.
Comeau D, Heaton K, Gordon A. Rheumatology and musculoskeletal problems. In: Rakel RE, ed. Textbook of Family Medicine. 8th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 32.
Ferri FF. Laboratory tests and interpretation of results. In: Alvero R, Borkan JM, Ferri FF, et al, eds. Ferri's Clinical Advisor, 2014. Philadelphia, PA: Elsevier Mosby; 2014:section IV.
Low ED. Nonpneumoccal streptococcal infections, rheumatic fever. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 298.
Nussenbaum B, Bradford CR. Pharyngitis in adults. In: Flint PW, Haughey BH, Lund LJ, et al, eds. Cummings Otolaryngology: Head & Neck Surgery. 5th ed. Philadelphia, PA: Elsevier Saunders; 2010:chap 13.
Reviewed By:Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
The information provided herein should not be used during any medical emergency
or for the diagnosis or treatment of any medical condition. A licensed medical professional
should be consulted for diagnosis and treatment of any and all medical conditions. Call 911
for all medical emergencies. Links to other sites are provided for information only -- they
do not constitute endorsements of those other sites. © 1997-A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
The Agency for Health Care Administration (Agency) and this website do not claim the information on, or referred to by, this site is error free. This site may include links to websites of other government agencies or private groups. Our Agency and this website do not control such sites and are not responsible for their content. Reference to or links to any other group, product, service, or information does not mean our Agency or this website approves of that group, product, service, or information.
Additionally, while health information provided through this website may be a valuable resource for the public, it is not designed to offer medical advice. Talk with your doctor about medical care questions you may have.