What point of care test do we use for a throat swab in respiratory illnesses?

Point-of-Care Testing for Throat Swabs in Respiratory Illnesses

For bacterial pharyngitis, the primary point-of-care test is the rapid antigen detection test (RADT) for Streptococcus pyogenes (Group A Streptococcus), which can be performed directly at the bedside or in the clinic. 1

Primary Testing Approach

Rapid Antigen Detection Test for Streptococcus pyogenes

• The rapid antigen test for Group A Streptococcus is the standard point-of-care test for throat swabs and can be performed by healthcare personnel at the point-of-care or transported to the laboratory. 1
• The test detects Group A streptococcal antigen directly from pharyngeal swabs using antibodies specific for the group A carbohydrate. 1
• Numerous commercially available direct antigen tests exist, varying in sensitivity and ease of use. 1

Age-Specific Testing Algorithm

In Pediatric Patients (Critical Caveat):

• If the rapid antigen test is negative and the test has a sensitivity of <80%, a second throat swab should be examined by a more sensitive direct NAAT or by culture to arbitrate possible false-negative results. 1
• Collect a dual swab initially to facilitate this two-step algorithm, recognizing that the second swab will be discarded if the direct antigen test is positive. 1

In Adult Patients:

• Secondary testing after a negative rapid antigen test is usually unnecessary. 1

Alternative Point-of-Care Options

Direct Nucleic Acid Amplification Tests (NAATs)

• Direct NAATs for Streptococcus pyogenes are more sensitive than rapid antigen tests and negative results do not require arbitration by a secondary test. 1
• The swab transport device must be compatible with the specific NAAT platform used. 1
• Several FDA-approved NAAT platforms are now available for point-of-care use. 2

Monospot Test for Viral Pharyngitis

• For suspected Epstein-Barr virus (EBV) infection causing pharyngitis, the Monospot test can be performed as a point-of-care test using 5 mL serum. 1
• A positive Monospot test is diagnostic for EBV infection and no further testing is required. 3, 4
• Up to 10% of Monospot tests are falsely negative, particularly in younger children. 1, 3, 4
• If negative but clinical suspicion remains high, EBV-specific serologic testing (VCA IgM, VCA IgG, EBNA antibodies) should be performed on the same sample. 3, 4

Important Clinical Considerations

Test Performance

• Rapid antigen tests have demonstrated sensitivities of approximately 79-95% and specificities approaching 100% for Group A Streptococcus. 5, 6, 7
• The positive predictive value is very high (88-100%), making the test excellent for ruling in GAS infection. 7
• The negative predictive value is also very high (97-99%), making it useful for ruling out GAS infection. 7

Common Pitfalls to Avoid

• Do not rely solely on clinical suspicion without laboratory confirmation, as clinical features alone are insufficient for accurate diagnosis of Group A streptococcal pharyngitis. 2
• In pediatric patients, never accept a negative rapid antigen test as final without confirmatory testing if the test sensitivity is <80%. 1
• Do not use throat swabs for EBV detection, as EBV can persist in throat secretions for weeks to months after infection and does not confirm acute infection. 3

Specimen Collection

• Use a pharyngeal swab collected from the posterior pharynx and tonsillar areas. 1
• Transport in a swab transport device at room temperature within 2 hours. 1
• The accuracy of rapid antigen tests does not depend on organism viability. 5