The differences and the benefits

 

The virus spread around the world in a few short months, and its variants continue to sweep the globe. The good news is that a robust testing program as part of an organization’s SARS-CoV-2 response can help mitigate the spread of the disease. Diagnostic testing can identify active coronavirus infection and inform proactive next steps, like quarantining, to protect the infected individual and close contacts.

As testing is critical to diagnose and contain the spread of the virus, there are multiple methodologies available to yield a coronavirus testing result. The two types of diagnostic tests discussed here are molecular lab-based PCR, which detects viral RNA, and antigen-based testing, which detects viral proteins (the antigen). PCR and antigen testing are described more fully below to help make strategic decisions regarding community testing, planning, and implementation.

Download COVID-19 PCR and Antigen Tests Infographic

antigen-tests-thumbnail

 

SARS-CoV-2 PCR and antigen tests: get the facts

 

Technology

There are different types of technologies used to test for SARS-CoV-2:

PCR test


  • Detect viral RNA
  • SARS-CoV-2 RNA is extracted from the sample (throat swab, nasal swab, or saliva sample)
  • PCR—a type of nucleic acid amplification test—is then used to detect the viral genome

Antigen test

  • Detect the antigen—in this case, viral proteins
  • The saliva sample or nasal swab sample is added to a surface coated with antibodies that bind to specific viral proteins; this is used to create a signal that detects the virus

When to use

PCR test

person
  • When you need accurate results with high confidence
  • Ideal for diagnostic and population surveillance testing, especially in a high-volume setting
  • If you have symptoms and a negative antigen test result, get a PCR test for confirmation.1 If you have symptoms or are asymptomatic and have a positive antigen test result, get a PCR test for confirmation.

Antigen test

antigen-clock
  • When you need convenience and speed to quickly determine if a person may have the virus
  • Ideal for point-of-care testing and screening high-risk congregate settings—not for asymptomatic populations 2,3

Accuracy

Accuracy takes into account sensitivity and specificity by measuring how the test can correctly identify if a sample is infected with SARS-CoV-2.

PCR test

pcr-tests2
  • PCR tests have are considered the “gold standard” for detecting whether the virus is present
  • Highly sensitive PCR tests can detect low viral loads, even in the absence of symptoms

Antigen test

antigen-sensitivity
  • In one study, an antigen test had a sensitivity of 64% in symptomatic cases, meaning 36% (~2 in 5) positive cases receive a negative result (known as false negatives)*
  • In the same study, the antigen test had a sensitivity of 36% in asymptomatic cases, meaning 64% (~3 in 5) of positive cases receive a negative result (false negatives)*

cdc.gov/mmwr/volumes/70/wr/mm7003e3.html

Turnaround time

PCR test

k
  • It can take as little as 24 hours to get results

Antigen test

antigen-clock
  • It can take up to 30 minutes to report out each individual result, especially if the result is negative

 

Testing technology and community needs

 

The decision to include PCR and antigen technologies in a testing program depends on the unique needs of the community. Importantly, community leaders should consider the organization's tolerance of a wrong answer and the acceptability of that risk: what are the potential downstream effects of allowing an infected individual into the community because of a false negative result? Does convenience outweigh accuracy?

A clear understanding of the testing options is the first step in designing a testing program that will help keep the community safe. PCR tests, the gold standard for SARS-CoV-2 testing, provide high accuracy and therefore high confidence in the test results. Antigen tests are convenient when only a few results are needed, which may be advantageous in the point-of-care setting.

Style Sheet for Global Design System