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