Accessible, accurate COVID-19 testing remains one of the most important tools for reducing the spread of the virus and learning more about potential variants. While multiple types of vaccines have become more available—and often receive the most publicity—testing remains critical to identify the most efficient ways to quarantine and stop the virus from spreading to others.
Multiple types of COVID tests exist. From rapid at-home tests to COVID tests that can take up to 72-hours to receive results, much of the difference in the time it takes to receive the results has to do with the type of testing. Which begs the questions: why are different tests being used, and what is the most accurate COVID test?
As is the case with most other viruses, the body reacts over a period of time once a person has been infected with COVID-19. There are general stages of infection, including contracting the virus, developing symptoms*, and reduction of symptoms, even when the body is still infected. This is why it became so important during the height of the pandemic to communicate exposure: once exposed, you could be carrying the virus even before displaying symptoms.
Testing can be more accurate depending on when it’s administered to someone potentially infected. Current evidence shows that, with COVID, testing is less accurate around 72 hours after exposure, and then increases in accuracy sometime between five to seven days after exposure. Evidence also shows that testing is most accurate when someone is displaying symptoms.
*Asymptomatic cases can occur with COVID-19.
There are two primary types of COVID tests: PCR (or molecular) tests, and antigen tests. Both look for evidence of infection, but do so in different ways. PCR looks for genetic material representing the virus, while antigen tests identify proteins that are produced when your body is fighting the virus. Both typically require a nasal or oral swab to collect a sample for testing.
These different types of testing require different analysis, and have slightly different rates of accuracy. What’s critical about PCR and antigen tests is learning if a patient is currently infected, specifically for quarantine purposes.
PCR tests detect genetic material that is representative of a COVID infection. There are three main steps to completing a PCR test.
Sampling: usually a nasal swab or deep nasal swab is used to collect a small amount of respiratory material from the patient. This is sent to a lab for testing (unless it is a rapid test).
Laboratory analysis: The lab proceeds with an extraction process which specifies the genetic material that would indicate infection.
Diagnosis: a thermal cycler is used to replicate target genetic material, which produces a fluorescent light when containing COVID, detectable by the PCR machine.
While some false-positives occur, PCR testing is the most accurate of all COVID tests.
Antigen testing is inexpensive, can be conducted at point-of-care or at-home as a self-test, and is applicable to people of any age. This makes antigen testing a perfect candidate for the widespread testing needed to harness a pandemic.
While antigen tests can generally produce a result within 15-30 minutes, and are cited as being highly accurate, the CDC still notes that it may be necessary to confirm antigen testing with laboratory-based NAAT (PCR) molecular test.
Rapid COVID 19 tests, which can produce a result within minutes of testing, are typically antigen tests. While incredibly convenient, rapid COVID test accuracy suffers due to the method; a sample is placed on a strip that changes color, but a high amount of the virus is required to activate the changing agent. This can produce false negatives.
Laboratory-tested results remain the most trusted and accurate—from either antigen or PCR COVID testing. They can achieve more nuanced results from even small trace amounts of the virus, and they have generally been able to learn more even from tests produced from asymptomatic or from patients not yet showing symptoms.
Rapid tests are helpful but aren’t as accurate. Laboratory results are more accurate, but they require sampling to be sent in, risking loss or insufficient sample size.
False positives or false negatives occur when patients are given incorrect results after COVID testing. The FDA has acknowledged that false results do occur, and they note that anyone conducting testing must adhere to the recommended ways of conducting COVID tests. Often, false positives and negatives occur due to when a test is conducted (stage of virus) or an insufficient sample
Software can have glitches, sampling can get mixed up during transportation, errors can occur with communicating testing results—false positives and negatives can occur during testing for a number of reasons. With widely available testing like the rapid COVID tests, laboratory analysis will remain crucial to continue to study results, and to be able to more finely-measure and test for COVID traces.
BioCollections Worldwide is a leading diagnostics and testing provider. We keep up to date with developments in testing and work to provide accurate, available testing—especially for COVID. With over twenty years’ experience, BioCollections was already looking into COVID-related testing developments prior to the full pandemic, and now we’ve made our tests available to the public.