ASO

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Also known as: ASLO
Formal name: Antistreptolysin O Titer

At a Glance

Why Get Tested?

To help determine whether you have had a recent strep infection with the bacteria group A Streptococcus; to help diagnose complications resulting from a strep infection such as rheumatic fever or glomerulonephritis, a form of kidney disease

When to Get Tested?

When you have symptoms such as fever, chest pain, fatigue and shortness of breath that suggest rheumatic fever or symptoms such as edema and dark urine that are associated with glomerulonephritis, especially when you recently may have had a group A streptococcal infection that was not diagnosed and treated appropriately

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

Antistreptolysin O (ASO) is an antibody targeted against streptolysin O, a toxic enzyme produced by group A Streptococcus bacteria. ASO and anti-DNase B are the most common of several antibodies that are produced by the body's immune system in response to a strep infection with group A Streptococcus. This test measures the amount of ASO in the blood.

Group A Streptococcus (Streptococcus pyogenes) is the bacterium responsible for causing strep throat and a variety of other infections, including skin infections (pyoderma, impetigo, cellulitis). In most cases, strep infections are identified and treated with antibiotics, and the infections resolve.

When a strep infection does not cause identifiable symptoms, goes untreated, or is treated ineffectively, however, complications (sequelae), namely rheumatic fever and a type of kidney disease (glomerulonephritis), can sometimes develop, especially in young children. These secondary conditions have become much less prevalent in the U.S. because of routine strep testing, but they still do occur. These conditions can cause serious complications such as damage the heart, acute kidney dysfunction, tissue swelling (edema), and high blood pressure (hypertension). The ASO test can be used to help determine if these are due to a recent group A strep infection.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Hammad, T. (Updated 2012 June 4). Antistreptolysin O Titer. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2113540-overview through http://emedicine.medscape.com. Accessed January 2014.

Delgado, J. and Fisher, M. (Updated 2013 September). Streptococcal Disease, Group A - Group A, Strep. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/StrepA.html?client_ID=LTD through http://www.arupconsult.com. Accessed January 2014.

Robert J Meador, R. and Russell, I. J. (Updated 2013 December 13). Acute Rheumatic Fever. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/333103-overview through http://emedicine.medscape.com. Accessed January 2014.

Parmar, M. (Updated 2013 April 3). Acute Glomerulonephritis. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/239278-overview through http://emedicine.medscape.com. Accessed January 2014.

(© 1995–2014). Antistrep-O Titer, Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/80205 through http://www.mayomedicallaboratories.com. Accessed January 2014.

Vorvick, L. (Updated 2012 May 15). Antistreptolysin O titer. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003522.htm through http://www.nlm.nih.gov. Accessed January 2014.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 916-918.

Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pg 1528.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO. Pp 98-99.

Greco, F. (2005 April 29). ASO titer. MedlinePlus Medical Encylopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003522.htm.

(2001 October). Antistreptolysin O (ASO) Reagent Set, A Latex Slide Test. Teco Diagnostics [On-line package insert]. Available online through http://www.tecodiag.com.

(2000 April). Trutest ASO. True-Medix Diagnostics, Inc. [On-line package insert]. Available online through http://www.truemedix.com.

Mylonakis, E. (2005 June 10, Updated). Rheumatic fever. MedlinePlus Medical Encylopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003940.htm.

Agha, I. (2004 January 19, Updated). Post-streptococcal GN. MedlinePlus Medical Encylopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000503.htm.

Cunningham, M. (2000 July). Pathogenesis of Group A Streptococcal Infections. American Society for Microbiology [On-line journal]. Clin Microbiol Rev. 2000 July; 13(3): 470-511. Available online at http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=10885988 through http://www.pubmedcentral.nih.gov.

Vorvick, L. (Updated 2008 August 12). Antistreptolysin O titer. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003522.htm. Accessed January 2010.

Chin, T. and Li, D. (Updated 2009 November 20). Rheumatic Fever. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/1007946-overview through http://emedicine.medscape.com. Accessed January 2010.

Delgado, J. et. al. (Updated 2009 November). Streptococcal Disease, Group A - Group A, Strep. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/StrepA.html# through http://www.arupconsult.com. Accessed January 2010.

Mayo Clinic Staff (2009 January 23). Rheumatic fever. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/print/rheumatic-fever/DS00250/DSECTION=all&METHOD=print through http://www.mayoclinic.com. Accessed January 2010.

Bhimma, R. (Updated 2010 January 7). Acute Poststreptococcal Glomerulonephritis. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/980685-overview through http://emedicine.medscape.com. Accessed January 2010.

Nainggolan, L. (2009 March 6). AHA Updates Advice on Strep Throat, Preventing Rheumatic Fever. Medscape Today from Heartwire [On-line information]. Available online at http://www.medscape.com/viewarticle/589223 through http://www.medscape.com. Accessed January 2010.

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 102-103.

Forbes, B. et. al. (© 2007). Bailey & Scott's Diagnostic Microbiology, 12th Edition: Mosby Elsevier Press, St. Louis, MO. Pp 277.

(April 21, 2008) University of Virginia Health System: Rheumatic fever. Available online at http://www.healthsystem.virginia.edu/uvahealth/peds_arthritis/rheumat.cfm through http://www.healthsystem.virginia.edu. Accessed February 2010.

(Updated April 13, 2009) Wallace, MR. Rheumatic Fever. Medscape eMedicine. Available online at http://emedicine.medscape.com/article/236582-overview through http://emedicine.medscape.com. Accessed April 2010.