Which COVID-19 test is best?

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Different methods of COVID-19 tests includes molecular and antigen tests

OVERVIEW

According to Yale Medicine, there are two different types of tests to diagnose COVID-19: molecular and antigen. The main difference between the two are in how they are processed. 

Molecular tests take longer, usually 1-7 days, because they are typically processed in a laboratory. Antigen tests, also known as ‘rapid tests’ are processed anywhere, and results take between 10-15 minutes. 

The “sensitivity” of a test measures the rate at which it delivers a positive result for people with COVID-19. The higher the sensitivity, the lower the false readings. Generally, the greater sensitivity is found within a deeper specimen collected from the nose or throat. 

According to Mayo Clinic, the accuracy of any COVID test depends on the thoroughness of the sample collection and the accuracy of the lab analysis. 

Results may also be affected by the timing of the test. If someone was tested on the day they were infected, there is a higher chance of a negative result since there are not enough COVID particles in your test sample. It is recommended to get a COVID test about 5 days after exposure. 

None of the COVID-19 tests taken will tell you if you have a variant, such as Delta or Omicron. Detecting variants requires genetic testing done in a lab. 

MOLECULAR TESTS

The PCR (polymerase chain reaction) is a popular molecular test that detects the COVID virus’s RNA. It looks for genetic material from the virus by using chemicals to clone millions of copies of DNA from a small sample. Therefore, the PCR test is considered extremely sensitive. 

There are many different methods of the PCR test: nasopharyngeal, mid-turbinate, anterior nasal swab, oropharyngeal (throat) swab, and saliva. 

The nasopharyngeal, mid-turbinate, and anterior nasal swab are the three methods for nasal collection. Usually, samples are obtained with a swab inserted into the nose. A nasopharyngeal test consists of a long swab inserted into the nostril to obtain fluid from the back of your nose. A mid-turbinate test involves collecting a sample by placing a swab straight, less than 1 inch, into the nose. The anterior nasal swab involves twirling a swab in a nose at least four times to obtain a sample. 

The oropharyngeal (throat) swab collects a sample from the back of the throat. PCR saliva tests collect spit in a container, but they are only offered at select locations. 

According to Harvard Medicine, molecular tests are typically analyzed in a laboratory. The results may be affected by the conditions in which the test was shipped to the laboratory, or the laboratory itself. 

Misleading results can occur due to many factors including inadequate laboratory experience, cross-contaminations, detection of unspecified coronaviruses, inactive or residual COVID-19 detections, and technical reasons relating to equipment and kits.

According to the Centers for Disease Control and Prevention (CDC), laboratory-based tests, like the PCR test, have a “generally high” test sensitivity.  

ANTIGEN TESTS (RAPID TESTS)

Antigen tests look for bits of protein from the COVID virus. These tests require a larger amount of the COVID virus to be considered positive compared to the molecular test. Thus, an antigen test has a higher rate of false negatives.  

Like the molecular test, a swab collects a sample from the nose or throat. The sample is self-applied to a testing cartridge or strip and the results show a colored line to indicate a positive or negative result. 

According to the CDC, antigen test sensitivity varies depending on the timing of the test. The test is considered to have “moderate to high” sensitivity when the test is taken with the maximum viral sample. 

For people who are asymptomatic, antigen tests produce more false negative results. The FDA recommends taking multiple tests over several days to improve the chance of catching asymptomatic infections. 

At-home tests that give instant results are antigen tests. However, there are molecular ‘at home tests’ that require mailing a sample to a lab. According to Yale Medicine, it is a good assumption that ‘at home tests’ are less accurate than antigen tests. 

WHICH TEST TO USE?

According to Harvard Health Publishing, the U.S. Food and Drug Administration (FDA) has granted emergency use authorization (EUA) for hundreds of COVID-19 diagnostic tests.

“During a public health emergency, the FDA can use its Emergency Use Authorization (EUA) authority to allow the use of unapproved medical products, or unapproved uses of approved medical products, to diagnose, treat, or prevent serious or life-threatening diseases when certain criteria are met, including that there are no adequate, approved, and available alternatives,” according to their website. 

The most accurate tests that diagnose whether you previously had COVID or currently have COVID are listed on the Emergency Use Authorizations for Medical Devices page. This list shows the EUAs issued for medical devices during the COVID-19 pandemic. The Emergency Use Authorization lists all EUAs issued by the FDA.

SUMMARY

Due to the higher sensitivity and accuracy of the molecular test, it is encouraged to take a molecular test rather than an antigen test. 

According to Yale Medicine, health care providers typically rely on molecular tests, especially when people have COVID-19 symptoms. Antigen testing is encouraged for quick results for general screening and surveillance.

According to Harvard Health Publishing,“If you experience COVID-like symptoms and get a negative PCR test result, there is no reason to repeat the test unless your symptoms get worse. If your symptoms do worsen, call your doctor or local or state healthcare department for guidance on further testing.”