How Accurate are Rapid Strep Tests?

With an estimated seven million Americans seeking medical treatment for sore throats annually, it’s a safe bet that as a nurse practitioner you will treat your fair share of patients with swollen glands and tonsils. Sore throats are often the first sign of an impending illness; but sudden and severe sore throats combined with fever are the telltale sign of a more serious, yet common illness known as Group A Streptococcus or strep pharyngitis. With just one in ten cases of pharyngitis caused by strep, how do you make an accurate diagnosis?

Accuracy in diagnosing strep throat versus pharyngitis caused by viral or other illnesses can mean the difference of avoiding several complications that can arise with your patient; most specifically the under-treatment or over-treatment of sore throats through the misuse of antibiotics.

Inappropriately prescribing antibiotics when a patient does not have strep leads to the ineffective treatment of viral pharyngitis and can produce harmful side effects to the patient. It may also contribute to antibiotic resistance rendering the drug useless in future illnesses when it’s truly needed. Conversely, patients infected with strep throat who are not treated with antibiotics are at risk for developing rare but serious complications such as glomerulonephritis, damage to heart valves, rheumatic fever and peritonsillar abscesses. In addition, failure to prescribe antibiotics when warranted increases the likelihood that the patient will transmit the infection to others.

Relying on symptoms and history alone may not be sufficient to properly differentiate the cause of pharyngitis. Clinical guidelines call for the use of a rapid strep test on patients who present with the symptoms associated with the illness as the diagnostic tool has been shown to be both sensitive and specific for detecting the presence of strep. Though the test provides the convenience of results within ten minutes, according to a recent study published in 2014 by Clinical Infectious Diseases, it’s estimated that rapid strep tests yield false negative results in up to 1 of every 4 cases. This means that more than 250,000 patients per year with strep pharyngitis may not receive antibiotics when a provider follows clinical guidelines recommending heavy reliance on the rapid test in making a diagnosis.

So what should you do if your patient presents with strep symptoms but the rapid strep test shows the absence of Group A Strep antigens? Though the results take 1 to 2 days as opposed to ten minutes, throat cultures can be an accurate back-up for identifying step throat, leading to proper treatment of patients whose cases might have been otherwise undetected. 

Because throat cultures can be very expensive for patients, it’s important to use your best judgment and only proceed with alternate testing if the patient’s symptoms warrant further investigation. Overall, nurse practitioners can rest assured that rapid strep tests are a helpful diagnostic tool. 

 

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