A Different Question About Our COVID Testing Regime

In responding to a global pandemic, how do we balance the competing aims of preserving our health and minimizing disruptions to our lives and livelihoods? This remains the central question to every relevant policy debate six months in. This week, however, this debate has come to an unsettling new stage: a conversation over whether our testing itself has been conducted in an overly cautious way.

Most of us, when we think of them at all, think of a COVID test as a binary process: Someone sticks a cotton swab way too far up your nose or down your throat, and a few days later you find out if you have it.

But getting from Point A to Point B requires an elaborate laboratory process—a process that’s predicated on at least one injection of human subjectivity. The tests in ubiquitous use around the country make use of a process called polymerase chain reaction (PCR), which rapidly multiplies viral RNA in a sample to bring it to a measurable level. It’s a time-tested, proven process.

But it isn’t a one-step process: The PCR process must be cycled multiple times in order to get the virus to that level of visibility. How many cycles are necessary varies from test to test, but the math of exponential multiplication means that the more virus-saturated a sample was to begin with, the fewer you’ll need before you see the results.