There are multiple types of tests available for individuals suspected of having COVID-19, each looking for different targets and using different technologies to detect SARS-CoV-2. The range of options can make understanding how tests compare confusing. In fact, a recent online survey found only 30% of people in the US know the difference between two of the most widely used tests: PCR and antigen . Here are some of the key differences, and perhaps surprising similarities, between these two commonly used test options.
1. How do they work?
Antigen tests identify proteins on the surface of the SARS-CoV-2 virus. These assays are designed using SARS-CoV-2 antibodies that bind to the corresponding viral antigens, if enough of the antigen is present.
Molecular tests, on the other hand, target genetic material specific to the virus. Reverse transcription polymerase chain reaction (RT-PCR) is a type of molecular test, where enzymes convert SARS-CoV-2 RNA to DNA and primers amplify, or make copies of, the genetic material so it can be detected. Amplification allows for even small amounts of the virus to be detected, unlike antigen tests that require enough of the target to be inherently present in the sample. Other molecular tests using nucleic acid amplification techniques, such as loop-mediated isothermal amplification (LAMP) and nicking endonuclease amplification reaction (NEAR), are also available.
2. Where are they available and who can administer them?
With an easy-to-use, portable dock that plugs into a standard wall outlet, the Accula test returns PCR results for COVID-19 within 30 minutes.
PCR tests often require a laboratory to process samples. Because of the need for specialized equipment, lab-based PCR tests are commonly restricted to medical settings, such as hospitals, pharmacies, and urgent care clinics. Samples are collected and either sent out for processing or managed by labs on site, if available.
Point-of-care antigen and molecular tests deliver results without needing to send samples to a lab. These options are used by healthcare providers, with some platforms also available over the counter (OTC) for direct consumer purchase and self-administration. Because they are fast, accessible, and relatively inexpensive, OTC antigen tests have been a common driver of school screening protocols  and are also being purchased by employers to test large employee groups before gatherings .
Due to the need for special equipment and limitations in processing a high volume of tests, lab-based PCR tests are typically restricted to medical settings, such as hospitals, pharmacies, and urgent care clinics. Samples are collected and either sent out for processing or managed by labs on site, if available. Rapid PCR options like Thermo Fisher Scientific’s Accula SARS-CoV-2 Test, however, have made reverse transcription, point-of-care PCR testing a possibility.
This system uses a small, mobile docking station that plugs into a standard wall outlet. The Accula Dock doesn’t require samples to be processed by a lab and, with a CLIA certificate of waiver, this system can be used outside of traditional healthcare networks. Because of their ease of use and accuracy, more schools and event coordinators in non-traditional healthcare settings are turning to rapid PCR systems like the Accula test for an efficient, reliable molecular diagnostic solution.
3. How are the tests administered?
During the early days of the pandemic, many COVID-19 tests required nasopharyngeal swabs, or samples from the upper part of the throat, behind the nose. These “brain tickler” tests were invasive and often painful. Thanks to evolving testing technologies, both molecular and antigen tests are now typically minimally invasive, requiring either an anterior nasal swab retrieved from just within the nostril or a small sample of saliva to generate results.
4. What is the typical turnaround time to results?
One of the biggest myths around COVID-19 test options is that PCR tests will always take much longer to get results than antigen tests. It’s true that lab-based PCR tests require processing with special equipment and can take hours to days to provide results, particularly if samples need to be sent off site for processing. Rapid PCR options like the Accula system, however, deliver results in approximately 30 minutes. This is closer to the time needed for rapid antigen tests, which are touted for their ability to deliver results within minutes.
5. How reliable are they?
Perhaps the most important factor to consider with any clinical test is the accuracy of the results it delivers. With individuals making day-to-day choices based on COVID-19 risk, it’s critical that these decisions are backed by results that can be trusted.
Based on the technique’s established accuracy, lab-based PCR remains the gold standard for COVID-19 testing. Rapid PCR tests like the Accula system are able to deliver accuracy and sensitivity that’s in line with lab-based PCR, with the added convenience of fast results that don’t depend on the lab.
Anterior nasal swabs for COVID-19 diagnosis are inserted just one inch into the nostril to collect a sample. This option is minimally invasive compared to the nasophangeal swabs that were required with many first-generation COVID-19 tests.
Comparatively, studies have found antigen tests to be less sensitive than PCR tests . Because of concerns around accuracy, pandemic protocols that involve antigen testing often point to a need for repeat antigen testing over time or confirmation of results through PCR. This staggered process can lead to delayed diagnoses and increased exposure risk.
Not all COVID-19 tests work the same way or deliver the same reliability of results. An understanding of how the range of available options differ, and in what ways they’re actually the same, is essential to making informed personal health decisions and developing effective public policies to fight the COVID-19 pandemic.
Disclaimer: The Accula SARS-CoV-2 test has not been FDA cleared or approved but has been authorized for emergency use by FDA for use by laboratories certified under the Clinical Laboratory Improvement Amendments (CLIA) of 1988, 42 U.S.C. §263a, that meet requirements to perform high, moderate, or waived complexity tests. The test is authorized for use at the Point of Care (POC), i.e., in patient care settings operating under a CLIA Certificate of Waiver, Certificate of Compliance, or Certificate of Accreditation. This test has been authorized only for the detection of nucleic acid from SARS-CoV-2, not for any other viruses or pathogens. The emergency use of this test is only authorized for the duration of the declaration that circumstances exist justifying the authorization of emergency use of in vitro diagnostics for detection and/or diagnosis of COVID-19 under Section 564(b)(1) of the Federal Food, Drug, and Cosmetic Act, 21 U.S.C. § 360bbb-3(b)(1), unless the declaration is terminated or authorization is revoked sooner.
Regulatory and Intended Use:
For Use under the Emergency Use Authorization (EUA) Only. For prescription use only. For in vitro diagnostic use.
- Khandker, S. S., Nik Hashim, N., Deris, Z. Z., Shueb, R. H., & Islam, M. A. (2021). Diagnostic Accuracy of Rapid Antigen Test Kits for Detecting SARS-CoV-2: A Systematic Review and Meta-Analysis of 17,171 Suspected COVID-19 Patients. Journal of clinical medicine, 10(16), 3493. https://doi.org/10.3390/jcm10163493