Behind the Science: How Rapid PCR testing Works

Describing how a PCR test works, how it is different from a rapid PCR test and how the test is applied to a sample.

COVID has made all of us more familiar with scientific terms and processes than we ever would have imagined, whether we like it or not. Some of them we know by now, others we’ve heard but don’t fully understand, and others — like rapid PCR tests — may be newer ideas that could use some explaining. And since COVID testing will continue to be a regular part of our lives, it’s helpful to understand these concepts.

What is an antigen test?

Antigen testing identifies any proteins that are present from a virus particle; it works better the more of the proteins there are, which means that a significant viral load must be present to detect COVID-19. Think of it as an “after-the-fact” test. The individual already has symptoms, and an antigen test can confirm that it is COVID-19. But because it requires a high volume of viral load to be able to detect the virus, antigen testing can be imprecise.

How accurate are antigen tests?

Studies have shown the accuracy of antigen tests to vary by maker, but that they generally can detect the coronavirus disease 80 percent of the time when two tests are conducted within 24-36 hours of each other. Positive test results from antigen tests are considered highly accurate, but antigen tests are also prone to produce false negative results, and the CDC recommends additional testing to confirm a negative result from an antigen test.

What is a PCR test?

PCR testing has become the preferred test for detecting COVID-19 because of its accuracy and its ability to detect virus early in asymptomatic people. PCR, which stands for polymerase chain reaction, allows for early detection of the virus, rather than requiring a high volume of the virus to already be present in someone, like antigen tests. This is especially helpful in preventing outbreaks of the virus.

How does a PCR test work?

The basic concept behind PCR testing is multiplication. Whereas the antigen test needs a lot of the virus to be present, a PCR test essentially can take a trace amount of the virus and multiply it to levels that are then easily detectable. The PCR process does this by copying a part of the DNA of the virus, enough to verify that the virus is present in the sample. To identify a virus within a sample, the testing process applies those primer “keys” to the sample and heats it (in a lab test) or exposes it to light (in a field test).

This process makes copies of the virus within the sample, though it’s worth noting that making these copies does not mean the test creates more of the actual virus: The SARS genome contains about 30,000 base pairs of DNA, and each PCR test uses about 100 base pairs to identify the virus, so there is no risk of creating more disease.

How accurate are PCR tests?

PCR tests are roughly 95 percent accurate, and unlike antigen tests, they are not prone to false negatives and the CDC advises they do not require additional testing to confirm negative results.

What is a rapid PCR test?

A rapid PCR test is what it sounds like: A faster way to produce a standard PCR test result. The standard PCR test uses a heating process to multiply the DNA in the sample. The rapid PCR test, as produced by One Health Labs uses a portable thermocycler that uses both heat and fluorescent molecules — the addition of fluorescent light allows One Health Labs’ real-time PCR technology to detect results while the test is still running, while the portability of the kit enables on-site testing and, therefore, the shortest possible turnaround time for results, which are as accurate as a standard PCR test.

The rapid PCR, or real-time PCR, is the on-site test available through One Health Labs.

“The real-time PCR thermal cycler, like the Biomeme Franklin, has some optics in it and some photo sensors that are detecting that buildup of light,” says Jesse vanWestrienen, Biomeme co-founder and biology lead. “Then we use algorithms to analyze that data to ultimately determine whether that sequence you’re trying to amplify is present or not.”

How do you prepare a sample for rapid PCR testing?

An ordinary nasal sample contains other elements besides the virus, so it must be purified before testing. Using Biomeme’s M1 Sample Prep, One Health Labs provides a fast, easy way to clean up a sample without lab equipment. The sample is placed in a lysis buffer to break open the virus at a cellular level. The resulting chemical reaction binds the individual’s DNA and RNA to a glass fiber column, separating the virus material from all the impurities. The column acts as a filter. After a series of washes, the virus RNA is separated into a solution and is ready to be tested (the chain reaction part of the process).

The purified DNA/RNA solution is added to a lyophilized (freeze-dried) test well. That test well is then placed into the thermocycler. The thermocycler is then started, and the PCR reaction begins that determines whether the virus is present. On-site results are available within an hour when using One Health Labs field-tested, disposable kits.

“Almost all PCR that’s been used in the pandemic is real-time PCR,” vanWestrienen says. “What makes it rapid is Biomeme’s technology – very easy to use, field-based kits with a portable thermocycler.”

Preventing spread of the virus is key to head off any potential outbreaks of the virus, now and in the future, which is why we at One Health Labs believe that accurate, easy-to-administer, on-site test kits are crucial to preventing outbreaks that hold the potential for adversely affecting communities and businesses.