Most tests for COVID-19 involve taking a swab sample from the back of the nose, throat, or both. But some tests require a blood sample.

These tests aim to find out if a person has, or has ever had, an infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This is the virus that causes coronavirus disease 19 (COVID-19).

A molecular or antigen test can tell whether a person currently has the infection, regardless of whether they have any symptoms.

A serological, or antibody, test shows whether the body has antibodies to the virus. It cannot show whether a person has an active infection. If antibodies are present, it suggests that the body has already dealt with SARS-CoV-2.

This article will explore how COVID-19 tests work, which ones are available, when to have a test, and how to find one.

Coronavirus resources

For more advice on COVID-19 prevention and treatment, visit our coronavirus hub.

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A test for a SARS-CoV-2 infection often requires a swab sample.
Image credit: Chip Somodevilla/Getty Images.

There are several ways to test for evidence of the virus. A person may have one of the following types of COVID-19 test.

Molecular tests

Molecular tests look for signs of a current infection.

A person performing a molecular test usually takes a sample from the back of the throat, the nose, or both using a long cotton swab. A person might take their own swab sample at home.

RT-PCR test

One type of molecular test for the virus that causes COVID-19 is a real-time polymerase chain reaction (RT-PCR) test. This is sometimes called a nucleic acid amplification test (NAAT).

This involves a healthcare professional collecting a sample and sending it to a laboratory for testing. The analysis can detect signs of the virus’s genetic material in the sample.

This test can confirm a diagnosis of COVID-19 if it identifies two or three specific SARS-CoV-2 gene sequences. If it identifies only one, it will produce an inconclusive result.

Antigen tests

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Ways of taking a swab for a COVID test: Check the test instructions to find out which location is recommended.
Illustration by Diego Sabogal

An antigen test is sometimes called a lateral flow test. It detects proteins produced by the virus. This is a rapid test that people can take at home using a small device that resembles a home pregnancy test.

After taking a sample using the swab provided, the person dips the swab in a vial of fluid. They then insert the swab, which now contains some fluid, into a small device.

As the fluid spreads through the device, a line should appear on a screen on the device. This is a control line that shows if the test is working correctly.

After some time — maybe 15 minutes, depending on the specific test — another line may appear. If this happens, the result is positive for the virus. If the second line does not appear, the result is likely negative.

Molecular tests can only help diagnose current infections. They cannot tell whether someone has had COVID-19 in the past and recovered.

Serological tests

These detect antibodies the body produces to fight SARS-CoV-2. The antibodies are present in blood and tissues of anyone who has recovered from COVID-19.

Serological tests require a blood sample.

While they are useful indicators of a past SARS-CoV-2 infection, these tests may also detect antibodies produced to combat other types of coronavirus. So if the result is positive, it does not necessarily mean that the person has had COVID-19.

In the U.S., tests are available at health centers and some pharmacies in every state. Some areas have dedicated testing centers. Schools, workplaces, and other organizations may also have testing programs.

Some people require a prescription for a test, and some tests are only available in certain locations. An at-home test may produce a result right away, or a person may have to send their sample to a laboratory for analysis. In some cases, a collection service is available.

Rapid tests, also called direct-to-consumer or over-the-counter tests, are also available for purchase online and in retail locations like pharmacies and grocery stores. Make sure that any such test has authorization from the Food and Drug Administration (FDA).

Until the COVID-19 Public Health Emergency (PHE) expires on May 11, 2023, tests are free of charge to everyone, regardless of their insurance status. However, if a person gets their test as part of a doctor’s visit, there may be costs.

When the PHE expires, private insurance companies will no longer be required to cover the cost of COVID-19 testing.

However, for people enrolled in state Medicaid programs, testing costs will continue to be covered until September 30, 2024.

For people enrolled in Medicare Part B, the cost of a COVID-19 laboratory test ordered by a healthcare professional will continue to be covered, but over-the-counter test kits will not be covered.

Depending on the available supply of COVID-19 test kits, the U.S. government may continue distributing them free of charge, according to the U.S. Department of Health & Human Services (HHS).

People can find COVID-19 testing resources in their state on the HHS website.

Not all tests are suitable for everyone. Contact a healthcare professional or visit the local health department’s website to learn about the available options and confirm which type of test is appropriate.

Learn more about at-home testing options here.

No test is 100% reliable, as the FDA note, and it is possible to have a false-negative or false-positive result. This may happen if the person takes the test incorrectly or takes it too soon after exposure to the virus.

If a person has a negative result, has not been exposed to COVID-19, and has no symptoms, they do not need to isolate.

However, the Centers for Disease Control and Prevention (CDC) recommend the person should continue to protect themselves, such as by staying up-to-date on COVID-19 vaccinations and moving indoor activities outside.

If the COVID-19 test result is negative but the person has symptoms, the CDC recommends isolating for at least five days. The test result may be a false negative.

If a person has a positive result, they should stay home for at least five days, and isolate themselves from other people in their home or wear a high-quality mask around them.

Isolation may end based on the following, according to the CDC:

  • After five days, as long as a person has no symptoms or had symptoms that are improving, and they have not had a fever for 24 hours without using medications.
  • If a person continues to have symptoms after five days, they should continue isolating until the symptoms improve and they have not had a fever for 24 hours without using medication.
  • People who experience moderate illness, such as difficulty breathing or shortness of breath, should isolate for at least 10 days.
  • If a person was hospitalized for COVID-19 or has a weakened immune system, they should consult a doctor before ending isolation.

Until at least 11 days after testing positive, a person should avoid being around those at risk of getting severely ill from COVID-19, and wear a high-quality mask indoors and when around other people.

However, if a person tests negative after taking two antigen tests 48 hours apart, according to the CDC they may stop wearing a mask before 10 days.

Antigen tests may be less accurate than RT-PCT tests. The FDA point out that if a person has symptoms but gets a negative result from an antigen test, it may be a good idea to have an RT-PCR test and self-isolate.

Whether an antibody test result is positive or negative, a person should continue to take precautions. The result does not guarantee immunity and does not mean that the person cannot pass on the virus.

As the CDC note, a person should consider testing if:

  • They have symptoms of COVID-19, such as a cough or fever, in which case they should get tested right away.
  • They have been in a setting where exposure may have occurred, such as a crowded train.
  • They are in a high-risk setting that requires a test.
  • They will be in contact with someone at high risk for severe COVID-19.

Learn about the different types of vaccines and their possible side effects.

If a person previously tested positive for COVID-19 within the last 30 days and has symptoms, they should use antigen tests. If they do not have symptoms, the CDC do not recommend testing.

If a person previously tested positive for COVID-19 within the previous 31 to 90 days, with or without symptoms, they should use antigen tests.

What are the symptoms of COVID-19?

The two main types of COVID-19 tests are diagnostic tests, typically involving a swab, and antibody tests, which usually require a blood sample.

A diagnostic test can show if a person has a current SARS-CoV-2 infection, and an antibody test can show if they have had one in the past and recovered.

In the U.S., insurance companies will no longer be required to cover the cost of tests after the Public Health Emergency for COVID-19 ends on May 11, 2023. However, based on the available supply of test kits, the U.S. government may continue distributing them free of charge.

COVID-19 testing resources for each state can be found on the HHS website.