Current Testing Standards
The current test for the diagnosis of COVID-19, as recommended by the United States Centers for Disease Control and Prevention (CDC), is a qualitative real time RT-PCR nasopharyngeal swab which detects the presence of specific segments of the SARS-CoV-2 genome. The current CDC test detects and amplifies two regions of the nucleoside coding genome, N1 and N2. A positive test is found when both segments are detected. An inconclusive test occurs when only 1 segment is detected, and a negative test occurs when both segments are not detected. RNA primers for amplification and detection of these genetic segments are available publicly on the CDC website.19 Internal testing by the CDC comparing these primers and probes for N1 and N2 against public domain nucleotide sequences found no significant homologies with the human genome, other coronaviruses, or human microflora that would lead to a potential false positive.20 Limits of detection by RT-PCR were also tested internally by the CDC. While detection thresholds varied according to different commercially available master mixes of enzyme, all assays were able to reliably detect concentrations of 10 copies/uL.20 Multiple laboratories within the United States including reference laboratories and private hospital groups have implemented this testing, made allowable by the FDA under an Emergency Use Authorization (EUA). The FDA has also approved an EUA for multiple other commercial entities and academic medical centers to offer molecular testing either modified from the CDC protocol or developed with unique primers.21 RT-PCR testing by other countries has targeted other sequences of the SARS-CoV-2 genome.22