How Does the Rapid Antigen Test Perform Compared to PCR for Detecting SARS-CoV-2?
BACKGROUND AND PURPOSE:
Antigen-based SARS-CoV-2 tests are quick and cheap, but how well these tests perform, especially compared to PCR-based testing, is not well known
Pray et al. (CDCMMWR, 2021) evaluated the performance of the Sofia SARS Antigen Fluorescent Immunoassay (FIA) (Quidel Corporation) compared with RT-PCR for SARS-CoV-2 detection among both asymptomatic and symptomatic individuals
Paired testing analysis
Two Wisconsin universities, between September 28 and October 9
Nasal swabs were collected and tested using the Sofia SARS Antigen FIA and real-time RT-PCR
Virus culture was attempted on all antigen-positive or real-time RT-PCR–positive specimens
1,105 total nasal swab pairs
Asymptomatic: 79% (871 pairs)
Among swabs from asymptomatic participants, the antigen test has
Positive predictive value (PPV): 33.3%
Negative predictive value (NPV): 98.8%
The antigen performance among symptomatic participants
Of the 73 antigen positive tests or PCR test positive swabs
Virus was isolated from 46.6% (34 swabs)
There were 2 false negatives (out of 18 antigen/PCR test pairs where antigen was negative, but the PCR test was positive)
Antigen testing for SARS-CoV-2 can be both inexpensive and fast, but these benefits must be weighed against the lower sensitivity and PPV of antigen-based tests
PPV and sensitivity are particularly lower in asymptomatic cases
The CDC suggests confirmatory PCR testing for symptomatic people with a negative antigen test
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