People use polymerase chain reaction (PCR) and rapid (antigen) tests to diagnose COVID-19. The tests can differ in their timing, accuracy, and results. A person should speak with a healthcare professional to discuss any concerns regarding symptoms or testing.

COVID-19 is a highly contagious disease caused by the SARS-CoV-2 virus, a type of coronavirus that emerged late in 2019.

It affects people differently, with symptoms ranging from mild to severe. However, most people with the virus will have mild to moderate illnesses and recover without medical attention.

Common symptoms include:

Learn more about COVID-19 symptoms and their progression here.

The virus spreads when a person breathes in the air with tiny particles or droplets containing the virus. Most of the symptoms appear 2–14 days after exposure. To detect COVID-19, people can test using polymerase chain reaction (PCR) swabs or rapid tests (antigen).

This article discusses the differences between PCR and antigen tests and answers frequently asked questions.

A person testing for COVID-19 from a drive-through test centreShare on Pinterest
Brandon Bell/Getty Images

To date, there have been more than 830 million tests in the United States since testing began early in 2020. The country currently has a positive rate of 4.3%.

The positive rate or positivity rate is the percentage of tests returning positive relative to the total number of tests.

The PCR and rapid tests are diagnostic tools that people and doctors can use to determine the presence of COVID-19 infection in a person.

They collect samples the same way for both tests, typically through a swab. They perform this by taking a sample from the back of the throat, the nose, or both using a long cotton swab.

Doctors can also collect saliva samples as a person can spit into a tube rather than using a nose or throat swab.

However, the main differences include:

  • the type of test and what it tests
  • the procedure
  • availability
  • costs and timings
  • accuracy
  • results

Type of test

A lateral flow test is another term for an antigen test. While medical experts have been using these terms interchangeably with COVID-19 tests, researchers were using lateral flow technology long before COVID-19.

An antigen test uses lateral flow technology to confirm the presence or absence of a pathogen or biomarker. Other terms for lateral flow tests include antigen test, dipstick, test strip, rapid test, and quick test.

A PCR test is a molecular test. The PCR technique allows scientists to generate millions of copies from a very small amount of DNA.

What it tests for

A lateral flow test looks for protein (antigen) pieces found at the virus’s surface. An antigen is a substance that stimulates the body to produce antibodies as an immune response.

The test strip contains antibodies that are specific to SARS-CoV-2. If antigens are present in the sample, the antibodies in the test strip bind to them, causing the colored line to appear in the test cassette.

In comparison, a PCR test detects the RNA or the genetic material that comes with the virus. A PCR test uses chemicals to “amplify” or reproduce millions of copies of genetic material so that it can trace even the smallest amount of COVID genetic material.

The procedure

Although people perform both tests in the same way, using a swab, the procedure itself differs.

For a PCR, a person or a healthcare professional will take a swab. Then, lab technicians run, process, and analyze the PCR sample in an equipped laboratory.

Antigen testing does not require training, and a person can take a sample using a swab and determine the result at home.

Read more about the testing procedures here.

Availability

Lateral flow tests are available, easy to use, and do not require special training. A person can buy them at pharmacies and supermarkets and self-administer the test at home.

Ease of use and fast turnover makes them ideal for mass testing. A 2021 study found antigen tests to have a promising performance for mass testing.

In contrast, PCR tests require special equipment and skilled laboratory technicians, and only large facilities can conduct many of these tests simultaneously.

Costs and timings

Due to the rigorous process of PCR tests, a person may have to wait for hours to days as lab technicians test their sample. This timing can vary by area and state. The PCR testing process also makes it more expensive.

On the other hand, antigen tests are relatively cheaper and have a much shorter turnaround time of 15–30 minutes.

Accuracy

Because PCR tests can trace small amounts of COVID genetic material, they are highly sensitive and less likely to generate false-negative results.

Rapid antigen tests may not be as accurate as PCR tests. A 2021 study found that an antigen test is likely to be more accurate in people with high viral loads. Another 2021 study found that antigen tests are more specific when a person already presents with symptoms.

While many studies show that antigen tests have a low sensitivity compared with PCR tests, further research states they have a high specificity or can detect people who do not have the disease correctly.

Learn more about different COVID-19 tests here.

Results

Since lateral flow tests do not amplify the material they are looking for, the sample needs to contain enough viral antigen for the test to detect it. This makes it less accurate and shows a false-negative result in the early stages of infection when a person is asymptomatic and after the acute phase of the disease when the viral load decreases.

The Food and Drug Administration also warned healthcare professionals that false-positive results might occur in antigen tests, especially when users do not follow the instructions.

A 2022 Canadian study found that around 0.05% of tests conducted in 537 workplaces had a false-positive result, which the authors attributed to manufacturing issues rather than faulty implementation.

The Centers for Disease Control and Prevention (CDC) recommend a confirmatory PCR test for people with symptoms who have a negative antigen test result.

On the other hand, the CDC state that PCR tests may render positive results weeks to months after the initial infection.

Do both tests check for all variants?

According to the World Health Organization, both PCR and rapid antigen tests can detect the Omicron variant and older variants.

When to test?

A person who shows symptoms should take a test immediately. A person who does not show symptoms but has had close contact with someone with COVID-19 should take a test at least five days after exposure.

People who will travel should follow the guidelines set by their destination countries.

Which test is right for you?

The type of test depends on the person’s situation and symptoms. A person who needs urgent results or is currently experiencing symptoms may take an antigen test to get an immediate result.

However, an antigen test may not provide an accurate result for people who are not experiencing symptoms.

People who have had exposure to the virus, or have been in high-risk areas, who need to undergo a medical procedure, or continue to have symptoms even with a negative antigen test, should take a PCR test.

An antigen test can also be helpful for people in isolation who want to check if they are still infectious.

How to order tests?

A person can buy antigen tests in local pharmacies and some online stores. PCR tests are only available in centers, facilities, and hospitals.

People can check their state health departments or local health departments for health centers and community-based testing sites that offer these tests for free.

What type of samples are there for COVID testing?

Healthcare professionals can obtain samples from the nose, throat, or mouth (saliva). There are three methods for collecting a sample through a nasal swab:

  • Nasopharyngeal: This method involves inserting a long swab to collect a sample from the back of the nose.
  • Mid-turbinate: This involves inserting a soft swab less than an inch (2 centimeters) into the nostril to collect a sample.
  • Anterior nasal (anterior nares) swab: This method involves inserting a swab at least half an inch, or 1 cm, into the nostril to collect a sample.

Other methods include collecting saliva into a sterile cap container or inserting a long swab at the back of the throat (oropharyngeal) to collect a sample.

How to understand COVID-19 test results

A positive viral test (PCR or antigen test) indicates that a person had COVID-19 at the time of testing. It may show one of the following results:

  • Detected: There is an active infection
  • Not detected: Results do not indicate an active infection
  • Indeterminate: This result occurs when there is not enough amplifiable material or substances in the specimen for analysis. Doctors may recommend retesting.

In an antigen test, two lines mean that the test detects the virus in the sample, while a single line (in the control line) indicates that the virus is not in the specimen.

PCR and antigen tests have their advantages and disadvantages. They differ in their procedure, accuracy, results, timing, skill requirement, price, and availability.

The best test to use would depend on the person’s purpose and current symptoms.

Antigen and PCR tests are both widely used to diagnose COVID-19. PCR tests appear to be more accurate in diagnosing COVID-19. However, antigen tests are also accurate and specific when a person already has symptoms.

Antigen tests are affordable and may be helpful in situations such as when a person needs serial testing, wants to know if they are still infectious, or needs quick results.