Why It Takes So Long To Get Most COVID-19 Test Results

After a slow start, testing for COVID-19 has begun to ramp up in recent weeks. Giant commercial labs have jumped into the effort, drive-up testing sites have been established in some places, and new types of tests have been approved under emergency rules set by the Food and Drug Administration.

But even for people who are able to get tested (and there's still a big lag in testing ability in hot spots across the U.S.), there can be a frustratingly long wait for results — not just hours, but often days. Even Sen. Rand Paul, R-Ky., didn't get his positive test results for six days and has been criticized for not self-quarantining during that time.

We asked experts to help explain why the turnaround time for results can vary widely — from hours to days or even a week — and how that might be changing.

It's a multistep process

First, a sample is taken from a patient's nose or throat, using a special swab. That swab goes into a tube and is sent to a lab. Some large hospitals have on-site molecular test labs, but most samples are sent to outside laboratories for processing. More on that later.

That transit time usually runs about 24 hours, but it could be longer, depending on how far the hospital is from the processing laboratory.

Once at the lab, the specimen is processed, which means lab workers extract the virus's RNA, the molecule that helps regulate genes.

"That step of cleaning — the RNA extraction step — is one limiting factor," says Cathie Klapperich, vice chair of the department of biomedical engineering at Boston University. "Only the very biggest labs have automated ways of extracting RNA from a sample and doing it quickly."

After the RNA is extracted, technicians also must carefully mix special chemicals with each sample and run those combinations in a machine for analysis, a process calledpolymerase chain reaction, which can detect whether the sample is positive or negative for COVID.

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