Strep Throat

  • Medical Author:
    John Mersch, MD, FAAP

    Dr. Mersch received his Bachelor of Arts degree from the University of California, San Diego, and prior to entering the University Of Southern California School Of Medicine, was a graduate student (attaining PhD candidate status) in Experimental Pathology at USC. He attended internship and residency at Children's Hospital Los Angeles.

  • Medical Editor: Steven Doerr, MD
    Steven Doerr, MD

    Steven Doerr, MD

    Steven Doerr, MD, is a U.S. board-certified Emergency Medicine Physician. Dr. Doerr received his undergraduate degree in Spanish from the University of Colorado at Boulder. He graduated with his Medical Degree from the University Of Colorado Health Sciences Center in Denver, Colorado in 1998 and completed his residency training in Emergency Medicine from Denver Health Medical Center in Denver, Colorado in 2002, where he also served as Chief Resident.

Quick GuideCommon Sore Throat vs. Strep Throat

Common Sore Throat vs. Strep Throat

How is strep throat diagnosed?

There are two common tests used to establish whether an individual with symptoms of strep throat infection has a strep throat. The traditional test, a throat culture, involves the doctor obtaining a swab from the back of the throat and tonsils. It takes approximately 36 to 48 hours to determine the presence or absence of the GAS bacteria. This test is considered the "gold standard" in diagnosing strep throat.

Many medical offices, clinics and hospital emergency departments use a rapid strep test (RADT - rapid antigen detection test) in an effort to provide a more timely diagnosis for their patients. The throat swab is obtained similarly to that for a traditional throat culture, but a RADT "kit" is employed to help determine the presence or absence of the strep bacteria. The turn around time is generally 10 minutes. The RADT is less precise when compared with a throat culture. Most RADT tests are about 95% accurate in determining the presence of strep bacteria. Most guidelines recommend that a negative rapid strep test be confirmed with a throat culture. Of note, antibiotic pretreatment prior to obtaining a throat swab for strep bacteria can interfere with throat culture results, and thus the ability to correctly diagnose and treat a strep throat infection. Antibiotic treatment prior to a rapid strep test is less likely to have a false negative result since the test is designed to document the presence or absence of the GAS bacteria. Residual dead bacteria in the patient may allow a positive result.

The above tests are designed to determine whether an individual currently has a strep throat infection. Sometimes it may be necessary to determine whether a patient has had a recent history of a strep infection. In that case, two blood tests are available: (a) an ASO (anti streptolysin O) titer, and/or (b) an anti DNase titer. The antibodies that these tests are sensitive to are not commonly present until a few weeks following an acute strep infection. These tests may be ordered when evaluating a patient who may have developed delayed complications (such as rheumatic fever or glomerulonephritis) after a strep throat infection. Continue Reading

Reviewed on 4/20/2015
References
REFERENCES:

American Academy of Pediatrics Red Book. Group A Streptococcal Infections. 2012: 668.

CDC.gov. Is it Strep Throat?

Pichichero, Michael. Group A Beta-hemolytic Streptococcal Infections. Pediatrics in Review. 1998; 19: 291-302.

Wald, Ellen. Antibiotic Treatment of Pharyngitis. Pediatrics in Review. 2001; 22: 255.

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