Clinical Comparison and Agreement of PCR, Antigen, and Viral Culture for the Diagnosis of COVID-19

The COVID-19 nasopharyngeal PCR (NP PCR) is limited by lack of specificity after previous illness, healthcare personnel collection, and discomfort. Superficial testing using antigen (Ag) tests or nasal PCR may be an alternative. One-hundred-and-fourteen risk-stratified patients were tested by culture, nasal PCR, NP PCR, and Ag testing. Twenty (48%) of the high preset risk and 23 (32%) of the low pretest risk were NP PCR positive. Compared with NP PCR, the sensitivity of nasal PCR, Sofia Ag, BinaxNOW Ag, and culture were 44%, 31%, 37%, and 15%. In the high risk group, the sensitivity of these tests improved to 71%, 37%, 50%, and 22%. Agreement between tests was highest between nasal PCR and both antigen tests. Patients who were NP PCR positive but antigen negative were more likely to have remote prior COVID-19 infection (p<0.01). Nasal PCR and antigen positive patients were more likely to have symptoms (p = 0.01).