At a Glance
Why Get Tested?
To determine if a sore throat is "strep throat" that is caused by group A streptococcus (GAS)
When to Get Tested?
When you have a sore throat that your doctor thinks may be due to a bacterial infection
A swab rubbed against the back of your throat and tonsils
Test Preparation Needed?
The Test Sample
What is being tested?
The bacterium Streptococcus pyogenes, also known as group A beta-hemolytic streptococcus or group A streptococcus (GAS), causes "strep throat," the most common bacterial cause of inflammation and soreness of the back of the throat (pharyngitis). Strep throat tests identify the presence of this bacterium as the cause of a sore throat.
While most sore throats are caused by a virus and will resolve without treatment within a few days, 5-15% of adults and 20-30% of children with sore throats have strep throat. It is important that these bacterial strep infections be promptly identified and treated with antibiotics. Strep throat is contagious and can spread to close contacts. If the infection is not treated, secondary complications may develop, especially in children. These complications may include rheumatic fever, which can damage the heart, and glomerulonephritis, which affects the kidneys. Because streptococcal infections are routinely diagnosed and treated, these complications have become much rarer in the United States, but they do still occur.
Symptoms of strep throat vary and can be similar to those caused by other infections. They may include:
- Sore throat
- Reddened (inflamed) throat with or without white or yellow spots
- A swollen, tender neck
- Loss of appetite
A rapid strep test and/or a throat culture is used to diagnose group A streptococci as the cause of these symptoms and allows the doctor to prescribe the proper antibiotics for treatment.
How is the sample collected for testing?
A doctor, nurse, or other health care professional uses a tongue depressor to hold down a person's tongue and then inserts a special swab into the mouth and rubs it against the back of the throat and tonsils. The swab may be used to do a rapid strep test in a doctor's office or clinic, or it may be sent to a laboratory. A second swab may be collected along with the first one. This extra sample is used to perform a throat culture as a follow-up test, when necessary.
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 should be performed before antibiotics are prescribed.
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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
(2012 September 10). Bad Sore Throat? It's Probably Not Strep, Most Likely Viral. IDSA [On-line information]. Available online at http://www.idsociety.org/2012_Strep_Throat_Guideline/ through http://www.idsociety.org. Accessed September 2012.
Shulman, S. et. al. (2012 September 9). Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis: 2012 Update by the Infectious Diseases Society of America. Clin Infect Dis. (2012) doi: 10.1093/cid/cis629. [On-line information]. Available online at http://cid.oxfordjournals.org/content/early/2012/09/06/cid.cis629.full through http://cid.oxfordjournals.org. Accessed September 2012.
Khan, Z. and Salvaggio, M. (2012 August 1). Group A Streptococcal Infections. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/228936-overview through http://emedicine.medscape.com. Accessed September 2012.
Delgado, J. and Fisher, M. (Updated 2012 September). 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 September 2012.
Mayo Clinic staff (2010 June 26). Strep throat. Mayoclinic.com [On-line information]. Available online at http://www.mayoclinic.com/print/strep-throat/DS00260/DSECTION=all&METHOD=print through http://www.mayoclinic.com. Accessed September 2012.
Ben-Joseph, E. (Reviewed 2011 October). The Scoop on Strep Throat. KidsHealth from Nemours [On-line information]. Available online at http://kidshealth.org/kid/ill_injure/sick/strep_throat.html# through http://kidshealth.org. Accessed September 2012.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 939.
Choby B. Diagnosis and Treatment of Streptococcal Pharyngitis. Am Fam Physician. 2009 Mar 1;79(5):383-390. Available online at http://www.aafp.org/afp/2009/0301/p383.html through http://www.aafp.org. Accessed September 2012.
(May 2, 2012) Center for Disease Control and Prevention. Get Smart: Know When Antibiotics Work, Sore Throat. Available online at http://www.cdc.gov/getsmart/antibiotic-use/URI/sore-throat.html through http://www.cdc.gov. Accessed September 2012.
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.
(2005 October 11). Group A Streptococcal (GAS) Disease (strep throat, necrotizing fasciitis, impetigo). CDC, Division of Bacterial and Mycotic Diseases [On-line information]. Available online at http://www.cdc.gov/ncidod/dbmd/diseaseinfo/groupastreptococcal_g.htm through http://www.cdc.gov.
Vincent, M., et. al. (2004 March 15). Pharyngitis. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20040315/1465.html through http://www.aafp.org.
Kazzi, A. and Wills, J. (2005 April 21, Updated). Pharyngitis. eMedicine [On-line information]. Available online at http://www.emedicine.com/emerg/topic419.htm through http://www.emedicine.com.
Gerber, M. and Shulman, S. (2004 July). Rapid Diagnosis of Pharyngitis Caused by Group A Streptococci. Clinical Microbiology Reviews, July 2004, p. 571-580, Vol. 17, No. 3 [On-line journal]. Available online at http://cmr.asm.org/cgi/content/full/17/3/571 through http://cmr.asm.org.
Homeier, B. (2005 September, Reviewed). Strep Throat. KidsHealth for Parents, Nemours Foundation [On-line information]. Available online at http://kidshealth.org/parent/infections/lung/strep_throat.html through http://kidshealth.org.
Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 912-913.
Forbes, B. et. al. (© 2007). Bailey & Scott's Diagnostic Microbiology, 12th Edition: Mosby Elsevier Press, St. Louis, MO. Pp 265-278.
Smith, D. S. (Updated 2008 September 3). Streptococcal screen. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003745.htm. Accessed May 2009.
Sharif, I. (2008 November). Strep Throat. TeensHealth, The Nemours Foundation [On-line information]. Available online at http://kidshealth.org/teen/infections/bacterial_viral/strep_throat.html# through http://kidshealth.org. Accessed May 2009.
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 May 2009.
Vorvick, L. (Updated 2009 March 14). Strep throat. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000639.htm. Accessed May 2009.
(2009 February 26). Diagnosing, treating strep throat key to preventing rheumatic heart disease. American Heart Association News Release [On-line information]. Available online at http://americanheart.mediaroom.com/index.php?s=43&item=682 through http://americanheart.mediaroom.com. Accessed May 2009.
Mayo Clinic staff (2008 June 26) Strep throat. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/print/strep-throat/DS00260/DSECTION=all&METHOD=print through http://www.mayoclinic.com. Accessed May 2009.