With the introduction of vaccines and an abundance of testing options, the initial frenzied rush to get tested for COVID-19 has subsided in the US. However, confusion about the different types of tests and their relative benefits remain. In this post, we detail some of the different COVID-19 testing options, their accuracy in predicting active COVID-19 infections, and scenarios where one test might be a better choice than the other.
There are currently two main categories of COVID-19 tests: diagnostic tests and antibody tests. We expand on each of these two categories below.
COVID Diagnostic Tests
Diagnostic tests show if a person has an active COVID-19 infection and depend on the presence of either SARS-CoV-2 genetic material (molecular tests) or a signature protein (antigen tests) that the virus produces. Samples for diagnostic tests are typically collected with a swab of the nose or throat, or by collecting saliva.
A molecular test looks for the RNA (genetic material) of SARS-CoV-2. The presence of viral RNA in a patient sample indicates a positive result. Examples of technologies used in the lab include nucleic acid amplification tests (NAAT) and polymerase chain reaction tests (PCR).
The US FDA has authorized some molecular tests to be used in traditional laboratory settings while others are authorized for use in a point-of-care (POC) setting. These POC tests are administered, processed, and interpreted at, or very close to, the school, corporate office, or event (e.g., basketball game, cruise ships, etc.). The time-to-results for molecular tests typically range from less than an hour in POC settings to 1-3 days when the results are shipped to an outside laboratory.
Molecular tests tend to be highly accurate and usually will not need to be repeated to confirm an active SARS-CoV-2 infection. Here at Seegene, we’ve developed the Allplex™ 2019-nCoV (SARS-CoV-2) Assay, a PCR test that simultaneously detects three target genes of SARS-CoV-2 in a single sample. It received Emergency Use Authorization (EUA) from the US FDA in April 2020.
An antigen test detects one or more specific viral proteins. Detecting these proteins indicates that the virus is present. Currently, most antigen tests are used in POC settings. They are often referred to as “rapid tests” as they typically provide results in less than one hour. Most at-home testing kits for COVID-19 are also antigen tests.
Although rapid antigen tests can be highly accurate, false negatives do occur. Thus, both positive and negative rapid antigen test results may need to be confirmed by a molecular test. Another limitation of rapid antigen tests is that they may not detect early SARS-CoV-2 infections when antigen levels are still building.
COVID Antibody Tests
Antibody tests or “serology tests” look for antibodies that have been produced in response to SARS-CoV-2. Samples are typically collected via a finger stick or blood draw from a vein.
When a person’s immune system encounters an infection for the first time, immune cells called B cells produce antibodies that can stave off a repeat infection. The human body also produces antibodies in response to vaccination. As a result, the presence of antibodies to a pathogen usually suggests the body has “seen” that infection before. Antibodies can take several days or even weeks to develop in a person’s bloodstream and will stay for months or sometimes years, after the fact.
Unlike the molecular tests or rapid antigen tests, antibody tests do not report if you have a current, active SARS-CoV-2 infection. This is because the test looks for the presence of antibodies to the virus and not for the virus itself. An antibody test only provides information that a person has likely had a SARS-CoV-2 infection in the past. Although antibodies are produced in response to vaccination, the US FDA does not currently recommend antibody tests to be used in assessing for immunity against COVID-19.
While researchers are still working to understand the full implications of a positive COVID-19 antibody test, it is possible that over time, the broad use of antibody tests and clinical follow-up will provide researchers with data on how people (and ultimately populations) develop immunity to SARS-Cov-2 and its variants. This in turn will inform preventive and/or treatment measures against SARS-CoV-2 in the years to come.
So Which COVID-19 Test Should You Get?
Health experts advise that if you are experiencing a fever, cough, loss of taste and smell, or any combination of COVID-19 symptoms, or have come into contact with someone who has the illness, you should get tested immediately regardless of your vaccination status.
From there, things get complicated. Should you get an at-home test that will give you a result in less than an hour? Or should you go to the closest testing site and wait for 1 to 3 days for a molecular test result? In most parts of the United States, testing is free if you are not looking for a “rush service,” or it will be covered by your health insurance plan.
For most people, the type of test they end up taking depends on access and availability.
Should you take an at-home test?
Currently, all COVID-19 home test kits are rapid antigen tests, which can be easily bought over the counter at a local pharmacy.
Rapid antigen tests however tend to have a higher rate of false-negative results. Thus, a negative result from an at-home kit may be sufficient if you don’t have any symptoms of COVID-19. However, if you have symptoms of the illness and your test comes back negative, a follow-up PCR or NAAT may be needed to confirm the results.
How about travel?
Many countries now require either proof of vaccination and/or a negative COVID-19 test to enter the country. But not just any test will do: the government may stipulate that a molecular PCR or NAAT test is needed. Countries and airlines are less likely to accept results from an at-home test, as they are typically less reliable and more prone to user error.
Since COVID-19 is a rapidly evolving pandemic, travel requirements for countries and airlines are constantly changing and can vary. Therefore, it is important to do your research before submitting samples for any type of pre-travel test.
Can current COVID-19 tests tell me which variant I have?
While most tests on the market cannot definitively tell which SARS-CoV-2 variant a person has without genomic sequencing, Seegene’s multiplex NovaplexTM SARS-CoV-2 Variants Assays can. These tests are currently for Research Use Only (RUO) and Not for use in Diagnostic Procedures in the United States. Researchers can use our line of PCR-based tests to detect variants of concern (alpha, beta, gamma, and delta variants) as well as variants of interest.
The COVID-19 pandemic has been unpredictable and ever-changing. COVID-19 testing is no different. While current testing modalities have proven useful thus far, it is possible that new (and improved) testing modalities will emerge over time. It is also likely that researchers will learn more about the COVID-19 disease and how people build immunity to it.
In the meantime, it is important to continue to take precautions to protect yourself and the people around you.
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