Group A Strep

Rapid Tests For Group A Strep

Should Back Up Cultures Be
Performed?

Being Able to diagnose strep throat while the patient is still in the office has been a convenience to physicians for over a decade, now. They have become much more reliable than they were when first approved for general use, but the culture remains the "gold standard" test for definitive diagnosis.

The American Academy of Pediatrics recommends  back up cultures for patients with a negative rapid test. The 2000 Red Book: Report on The Committee on Infectious Diseases says "Several rapid diagnostic tests for GAS pharyngitis are available. Most are based on nitrous acid extraction of group A carbohydrate antigen from organisms obtained by throat swab. Although
the method for these test vary, their sensitivities and specificities, in general, are similar when carefully performed, including rigorous attention to technique and use of controls. The specificities of these test generally are very high, but the reported sensitivities vary considerably.
As with throat cultures, the accuracy of these tests is highly dependent on the quality of the throat swab specimen, which must contain pharyngeal and/or tonsillar secretions, and on the experience of the person performing the test. Therefore, when a patient suspected on clinical grounds of having GAS pharyngitis has a negative rapid streptococcal test, a throat culture should be obtained to ensure that the patient does not have GAS infection. Because of the very high specificity of these rapid tests, a positive test result does not require throat culture confirmation."*

The American Heart Association has a similar recommendation, suggesting the use of back up
cultures when rapid test results are negative.

* 2000 Red Book: Report Of The on Infectious Diseases 25th Edition American Academy of Pediatrics