Rapid Strep Test

The rapid strep test is a way to see if a person's sore throat is due to the bacterium Streptococcus— that is, whether the person has strep throat or simply a virus. It is a relatively inexpensive and quick test that, when used in combination with informed decision-making about a person's symptoms, can help guide the decision about whether they need antibiotics.

Description

The rapid strep test consists of a swab that is tickled against the tonsils for a few seconds, then placed into a plastic holder and submerged under a few drops of a test liquid. After a few minutes, a line shows up on an attached card that indicates whether or not strep is present.

Why Rapid Strep Test Is Done

The rapid strep test is done because it is important to know whether a person's sore throat is one of the 10% or so that is caused by Streptococcus or if it is due to a virus. If the person has strep throat, he or she should receive antibiotics to prevent complications. If they do not, then it is very important that they avoid taking antibiotics.

Another way to tell the difference is to use a culture, or grow the bacteria in the throat and see if strep emerges or if normal throat bacteria grow. The disadvantage to cultures is that they are more expensive and they take several days. (However, waiting for results will still leave enough time to treat the strep infection and avoid potentially serious, preventable complications.)

How Rapid Strep Test Is Done

The doctor or medical assistant wipes the back of the throat with a long cotton swab. While a strep screen can tickle and can cause a patient to gag or perhaps cough, it is not painful and lasts only a few seconds.

The swab is then placed in a plastic holder and wetted with a fluid. After a few minutes the test results show up on an attached piece of cardboard. A positive test result means strep is present in the throat. A negative result means strep isn't present.

Benefits

The benefit to a rapid strep test is that it is fast and inexpensive compared to cultures. Importantly, the test is both sensitive and specific, meaning that its results correspond well with the actual presence or absence of the streptococcal bacteria.^[1]

Risks

The risk of getting a rapid strep test is extremely small; it is very safe. A child might vomit slightly from the gag reflex.

Effectiveness

The effectiveness of a strep test depends in part on how it is used.

It is important to know when a strep test (or any test) is not appropriate. According to the CDC, it should only be done if a person has at least two of the following four symptoms: white or yellow matter on the tonsils (tonsillar exudates), fever, painful swollen glands in the front of the neck, and a lack of coughing.^[2] Children or adults with two or more of these symptoms may be screened with the rapid strep test. If the patient has only one of the four symptoms, a positive strep test is not likely to be due to strep throat (a false positive result); therefore, the test should not be done in such patients, as they are almost certain to have a virus rather than strep throat.

A positive rapid strep screen or throat culture, in the face of likely symptoms, means the patient probably has strep throat and should take antibiotics. A rapid strep screen can offer results in minutes, whereas a throat culture takes two to three days. Sometimes, depending on the severity of the patient's symptoms and other specific circumstances, antibiotic treatment is started before the culture results.

If the rapid strep screen is negative, but the person has several of the above symptoms, a throat culture is often done. This is because the rapid test can miss some cases of strep throat. Often, the doctor will take both samples at once, in case the culture is needed. That way, the patient only feels uncomfortable once.

If the throat culture results are negative for strep, antibiotic treatment can be avoided or stopped. This reduces the risks from unnecessary antibiotic treatment. A negative throat culture usually means that a virus is probably the cause of the sore throat. Viruses cause about 90% of sore throats and are a much more common cause than strep.

Alternatives

Two alternatives to the rapid strep test are (1) a throat culture, which also involves rubbing a swab against the back of the throat, and (2) no testing, a choice that is often reasonable if a patient has several of the telltale symptoms of strep throat discussed above.

References

1. ↑ Sheeler RD, Houston MS, Radke S, Dale JC, Adamson SC. Accuracy of rapid strep testing in patients who have had recent streptococcal pharyngitis. J Am Board Fam Pract. 2002 Jul-Aug;15(4):261-5. Abstract | PDF
2. ↑ Snow V, Mottur-Pilson C, Cooper RJ, Hoffman JR; American Academy of Family Physicians; American College of Physicians-American Society of Internal Medicine; Centers for Disease Control. Principles of appropriate antibiotic use for acute pharyngitis in adults. Ann Intern Med. 2001 Mar 20;134(6):506-8. Citation | PDF