For diagnosing SARS-CoV-2, a PCR test starts with a nasopharyngeal swab, which looks like a long Q-tip that draws mucus from the back of a patient’s nasal cavity where it meets the throat. This swab goes in a vial and is shipped to an FDA-approved central lab facility. There, technicians use reagents to extract any viral RNA. An enzyme called reverse transcriptase converts the RNA to a complementary sequence of DNA, which can be replicated many times over to make it easy to detect. To accomplish this replication and detection, technicians—or automated machines, in most cases—add additional reagents that include…