PCR Diagnostic Test
The Polymerase Chain Reaction (PCR) test is considered the current gold standard in qualitative detection of the SARS-CoV-2 virus. It is extremely sensitive and specific by nature, but must be performed in a laboratory.
PCR tests look for pieces of SARS-CoV-2, the virus that causes COVID-19, in the nose, throat, or other areas in the respiratory tract to determine if the person has an active infection. A special lab machine, called a “thermal cycler” or “thermocycler,” duplicates a certain strand of genetic material hundreds of millions of times. This allows a relatively small specimen from a nasal swab to be photocopied over and over until any sequence of SARS-CoV-2 is easily spotted.
PCR tests are sensitive to super-low levels of viral RNA that can persist in the body for days or weeks beyond the period in which one is contagious. Such sensitivity is useful for clinical diagnosis, but not at all for public health screening. And a PCR test is simply too slow: it returns results in days when minutes matter, for we need to know now who is and who is not contagious.
- Speed is decidedly more important than sensitivity.
- Frequency of testing is decidedly more important than sensitivity.
- A testing protocol with a rapid antigen test—a speedy and viral-contagiousness-sensitive test—can reduce and maintain infections close to zero; a slower viral-presence-test cannot.
The best-in-class PCR tests can reliably detect SARS-CoV-2 in just a few hours with consistent reliability. However, PCRs require labs, technicians, and materials which have been in short supply across the United States, leading to testing delays and limitation of tests to those already in a symptomatic, and therefore infectious, state.
“There’s been a shortage of supplies to do the lab-based, molecular (PCR) testing as the case numbers go up on the mainland; three of our labs here in Hawaii have had a shortage. It would be good if there was an alternative technology that would supplement our testing capacity. “
-Edward Desmond, Hawaii State Department of Health laboratories administrator
Antigen Diagnostic Tests
Antigen tests look for proteins that make up the SARS-CoV-2 virus to determine if a person has an active infection. In most cases, a nasal or throat swab is taken by a healthcare professional and then tested. Recently developed antigen tests may be able to be processed while the person waits, but it is more likely that the swab needs to be sent to a lab for testing.
Antigen tests are typically faster and less expensive than PCR tests, but they are also less sensitive. This means that an antigen test may produce false negative results from people with lower concentrations of the virus.
Rapid antigen tests can overcome this issue through affordable, persistent testing. At lower viral load levels, antigen tests cannot completely rule out active COVID-19 infection. Health care providers may order a molecular test if your antigen test shows a negative result but you have symptoms of COVID-19.
“Even if you miss somebody on Day 1, if you test them repeatedly, the argument is, you’ll catch them the next time around.”
-Omai Garner, director of clinical microbiology in the U.C.L.A. Health System.
Most antigen tests still do require trained technicians to process results using lab equipment. Some of this equipment may be available ‘on-site’ within testing facilities and pop-up laboratories in certain states, but for other antigen type tests, specimens must be mailed to a specific laboratory or central processing location. While results can be delivered quickly, sometimes in under one hour, the processing of these tests means that a person must report to a point of care, or deliver their sample to a point of care.
These limitations can impose delays or strains on repetitive or regular testing regimes.
LAMP Diagnostic Tests
LAMP stands for Loop-mediated isothermal Amplification, and a LAMP procedure was was recently developed for detecting the presence of SARS-CoV-2 in subjects. The procedure uses saliva or nasal specimens, RNA extraction, reverse transcription, and loop-mediated isothermal amplification. The results are then interpreted via colorimetric read-out.
Colorimetric analysis is a method of determining the concentration of a chemical element or chemical compound in a solution with the aid of a color reagent.
The LAMP method requires fewer materials and less equipment overall when compared to a Lab PCR test, solving the availability and supply chains problems associated with PCR test materials. Results from novel LAMP processes can return results in 1-3 days at volume, but may be slightly less sensitive and accurate than PCR.
“It opens up the flexibility of the supply chain to this PCR alternative, which is nice. But it doesn’t overcome some of the common barriers to testing,”
-Matthew Lalli, a researcher studying genomics technologies at Washington University in St. Louis.
Loop-mediated isothermal amplification has been around since the 90s when it was created in Japan as a less time/material-intensive alternative to polymerase chain reaction-based tests. The key difference is that a laboratory PCR repetitively heats and cools a sample at precise intervals (thermo cycling) whereas LAMP does not.
Similar to a pool pH test, the LAMP procedure often calls for a color-change compound to be added to the specimen, changing from pink to yellow in different conditions (i.e. the presence of the virus) making it very easy to read results.
Rapid Covid-19 Tests
Health experts argue that when it comes to testing, we need speed and regularity, not hypersensitivity with scarcity. Rapid, inexpensive tests can detect cases that would otherwise be missed, allowing people to isolate before they infect others.
It’s true that rapid tests are less sensitive than PCR tests, meaning that they may sometimes fail to detect when the virus is present. However, many doctors and scientists agree that rapid tests are sensitive enough when it matters most: when a person’s viral load is high enough that you are contagious.
Speed and ease of use, when combined with affordability, availability, and a regular-interval testing regime makes rapid COVID tests ideal for routine public health screening.
The ASSURE rapid tests eliminate the need to deliver samples to collection points or mail samples and then wait for results. ASSURE also removes the need for expensive equipment for processing.
The ASSURE tests use swab specimen collection and a simple test cassette, like a home pregnancy test. A swabbed specimen is collected, mixed with buffer solution, and applied to a test cassette. Results show up in just a few minutes, indicated by a red line control line and positive line if Covid-19 is detected.