COVID-19 testing 101

Learn how different tests help to combat SARS-CoV-2 (COVID-19)
and when they should be used.

Use the right test at the right time

Our interactive Right Test Right Time Tool will help determine which COVID-19 test
is right for your needs.

What’s the difference between
COVID-19 tests?

Learn how each test works and why each one has a valuable role to play in the fight against the COVID-19 pandemic.
Testing Types 101

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Diagnostic (viral) tests show active infection

When
To Use The Test

How The
Test Is
Done

Diagnostic (viral) tests show active infection
Polymerase Chain Reaction (PCR) Test

PCR testing is a type of molecular test used to accurately detect active infections. It’s the gold standard for testing. It is the most commonly used nucleic acid amplification test (NAAT).

  • People with symptoms
  • People exposed to
    COVID-19
  • People without symptoms who live or work in a high-risk outbreak setting
  • As a confirmatory test when a rapid antigen test delivers a positive result

Saliva or swab from the nose or throat

Diagnostic (viral) tests show active infection
Antigen Test

Antigen testing is used to identify active infections. It is a fast, reliable, and affordable alternative to PCR testing.

  • People with symptoms
  • People without symptoms as part of a screening program

Swab from the nose or throat

Antibody tests show past infection
Antibody Test

Antibody testing shows if a person’s body has had an immune response to
COVID-19.

  • To detect a past COVID-19 infection
  • To check if people have developed an immune response to COVID-19 infection
  • To help make clinical decisions after an infection

Blood from the arm or finger stick

Diagnostic (viral) tests show active infection

When
To Use The Test

How
The Test Is Done

Polymerase Chain Reaction (PCR) Test

PCR testing is a type of molecular test used to accurately detect active infections. It’s the gold standard for testing. It is the most commonly used nucleic acid amplification test (NAAT).

  • People with symptoms
  • People exposed to COVID-19
  • People without symptoms who live or work in a high-risk outbreak setting
  • As a confirmatory test when a rapid antigen test delivers a positive result

Saliva or swab from the nose or throat

Diagnostic (viral) tests show active infection

When
To Use The Test

How
The Test Is Done

Antigen Test

Antigen testing is used to identify active infections. It is a fast, reliable, and affordable alternative to PCR testing.

  • People with symptoms
  • People without symptoms as part of a screening program

Swab from the nose or throat

Antibody tests show past infection

When
To Use The Test

How
The Test Is Done

Antibody Test

Antibody testing shows if a person’s body has had an immune response to COVID-19.

  • To detect a past COVID-19 infection
  • To check if people have developed an immune response to COVID-19 infection
  • To help make clinical decisions after an infection

Blood from the arm or finger stick

Source: Adapted from County of Los Angeles Public Health. Types of Coronavirus Tests. http://publichealth.lacounty.gov/acd/docs/COVIDTestTypeTable.pdf. Accessed January 7, 2021.

Testing Types 101

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PCR testing: the gold standard

PCR, the most commonly used nucleic acid amplification test (NAAT), is considered the gold standard for COVID-19 diagnosis. Why? Because it is unlikely to return incorrect results.1,2 The advantage of PCR testing is its accuracy, but its disadvantages include its relatively high cost and potentially longer turnaround times. That means we need more than PCR testing alone when there is a surge in cases.

Antigen testing: a fast first step

Antigen testing is a reliable and scalable way to quickly identify active COVID-19 infections at the point of care. Due to evolving variants and unvaccinated populations, antigen testing remains an important tool to limit the spread of COVID-19.

Scalable

An easy option to expand COVID-19 testing capacity and lower the cost of screening and diagnosis.

Reliable

A trusted first step in detecting infection that can be confirmed by a PCR test if needed.

Actionable

An important part of safety protocols that helps prevent spread, so we can go about 
daily activities responsibly.

Scalable

An easy option to expand COVID-19 testing capacity and lower the cost of screening and diagnosis.

Reliable

A trusted first step in detecting infection that can be confirmed by a PCR test if needed.

Actionable

An important part of safety protocols that helps prevent spread, so we can go about 
daily activities responsibly.

Antigen tests are often faster and are generally lower cost than PCR tests. This makes them a practical option for screening large populations of people without symptoms—like students in universities. In this way, antigen tests reduce the strain on laboratories across the nation because they free up capacity for critical PCR testing of patients with symptoms.
Antigen tests produce few false positives and false negatives, which makes results highly reliable. They also have a faster turnaround time compared to PCR tests.5 That’s why the CDC suggests frequent antigen testing (every 3-5 days5) for early identification and control of outbreaks in shared living situations—like in nursing homes. Antigen tests are less accurate than their PCR counterparts; therefore, in cases when the test results are not consistent with the patient’s symptoms or exposure, PCR testing is needed to confirm. 
Antigen testing offers actionable results that complement safety measures like social distancing and wearing masks. It is more accurate than temperature checks and can be widely used for fast, frequent screening of people without symptoms. With antigen screening, it is possible to detect and isolate infected individuals so more people can return to work, school, and other social settings responsibly.

Antibody testing: providing insight

Antibody testing, also known as serology testing, plays an important role in tracking the spread of COVID-19, identifying people who have had an immune response, and understanding personal health. Antibody testing can help inform decisions about resuming daily activities.

Surveillance

Insights for public
health efforts.

Screening

Enhance the scalability
and affordability of
screening programs.

Improve health outcomes

Inform ongoing
care to improve
health outcomes.

Surveillance

Insights for public health efforts.

Screening

Enhance the scalability and affordability of screening programs.

Improve health outcomes

Inform ongoing care to improve health outcomes.

Studies suggest that actual infections can be 6–24 times more than reported cases.4 Antibody testing captures prior infections to show a more complete picture of community infection and inform effective public health policies. Testing also can estimate how much of the population has not yet been infected, helping public health officials plan for future healthcare needs.5
Antibodies to SARS-CoV-2 (COVID-19) virus remain active in the body for months9 and may provide protection from further infection. By identifying people with antibodies who may not need ongoing screening, we can more efficiently use antigen and PCR testing resources and make screening programs more scalable and affordable. 
Evidence shows there can be long-term health effects from COVID-19 disease. Therefore, knowing if someone was previously infected with COVID-19 is an important part of their medical history. Antibody testing may be valuable to physicians treating individuals at higher risk of severe clinical outcomes from COVID-19, such as the elderly and those with diabetes, COPD, or cardiovascular risks.

Access more COVID-19 resources

Review information that can help you and others understand the importance
of comprehensive testing.
  1. Park GS, Ku K, Baek SH, Kim SJ, Kim SI, Kim BT, Maeng JS. Development of reverse transcription loop-mediated isothermal amplification assays targeting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). J Mol Diagn. 2020;22(6):729-735.
  2. Shen M, Zhou Y, Ye J, Abdullah AL-maskri AA, Kang Y, Zeng S, Cai S. Recent advances and perspectives of nucleic acid detection for coronavirus. J Pharm Anal. 2020;10(2):97-101.
  3. Centers for Disease Control and Prevention. SARS-CoV-2 antigen testing in long term care facilities. https://www.cdc.gov/coronavirus/2019-ncov/hcp/nursing-homes-antigen-testing.html. Updated January 7, 2021. Accessed February 1, 2021.
  4. Havers FP, Reed C, Lim T, et al. Seroprevalence of Antibodies to SARS-CoV-2 in 10 Sites in the United States, March 23-May 12, 2020. JAMA Intern Med. 2020;180(12):1576–1586.
  5. Centers for Disease Control and Prevention. COVID-19 Serology Surveillance Strategy. https://www.cdc.gov/coronavirus/2019-ncov/covid-data/serology-surveillance/index.html. Updated February 12, 2021. Accessed July 12, 2021.
  6. Wu F, Wang A, Liu M, et al. Neutralizing antibody responses to SARS-CoV-2 in a COVID-19 recovered patient cohort and their implications. medRxiv preprint. 2020. https://doi.org/10.1101/2020.03.30.20047365. Accessed February 5, 2021.
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Antibody testing determines the presence of antibodies that recognize markers of SARS-CoV-2, the virus that causes COVID-19, indicating that the body previously had been infected. In many diseases, the presence of antibodies confers immunity, but scientists have not verified if this is true for COVID-19. See the glossary section of our website to learn about the difference between Nucleocapsid Protein Antibody Tests and Spike Protein Antibody Tests.

PCR testing is used to accurately detect active infections. It is a type of molecular test and considered the gold standard for testing. PCR is the most commonly used nucleic acid amplification test (NAAT).

Antigen testing is used to identify active infections. It expands testing capacity as a fast, reliable, and affordable screening and diagnostic option.