Learn the difference between Antigen and PCR test

Throughout the pandemic we've heard non-stop about ANTIGEN AND PCR tests. But truly, what are the differences and why does it matter?

It is likely that you have been tested for COVID-19 given that over 800 million tests have been reported to the CDC as of February 2022.  This number does not include any tests taken that were performed and not reported to the CDC; like with self-administered home testing.  But do you know which type of COVID-19 test you had and understand the different types of tests that are available?

January 2022 

There are different types of tests –diagnostic tests and antibody tests.

Diagnostic tests  indicate if you have an active COVID-19 infection and therefore need to take steps to quarantine or isolate yourself from others. Samples for diagnostic tests are typically collected with a nasal or throat swab, or from saliva collected by spitting into a tube.

Molecular and antigen tests are types of diagnostic tests that can detect if you have an active COVID-19 infection. 

Antibody tests look for antibodies in your immune system produced in response to SARS-CoV-2, the virus that causes COVID-19.  Antibody tests should not be used to diagnose an active COVID-19 infection.

Antibodies can take several days or weeks to develop after you have an infection and may stay in your blood for several weeks or more after recovery. Samples for antibody tests are typically blood from a finger stick, or blood drawn by your doctor or other medical personnel.

Antigen and PCR tests can detect if you have an active COVID-19 infection

What is a pcr test? ​

what is a PCR test?

The PCR (Polymerase Chain Reaction) is a test which can detect the virus’s genetic material. They are also referred to as diagnostic tests. They are primarily taken via nasal swabs; however, some are done as a saliva test, which is less common. The collected sample is then converted into DNA, where it can be positively identified if present in the sample.

Standard PCR tests must be sent to a lab for processing and may take 1 – 3 business days to return results. 

This test is still needed to enter some international destinations. 

what is antigen test

 

Antigen tests are often also referred to as viral or rapid tests. An antigen test detects a protein coating the surface of the SARS-CoV-2 virus. Typically, these are collected through nasal swabs and then placed into a solution to identify the virus. These types of tests can produce results in as little as fifteen minutes. Because antigens tests are affordable and don’t need to be sent to a lab, they are ideal for large groups and events, as they allow many individuals to get tested in a short time frame.

What is antigen test​
Covid-19 tests types

Type of samples for Antigen and PCR test

These are the most common sample types:

Swab samples use a swab, Q-tip like stick or bud, to collect a  specimen from the nose or throat. The types of samples include:

Anterior Nares (Nasal) – takes a sample from just inside the nostrils

Mid-turbinate – takes a sample from further up inside the nose

Nasopharyngeal – takes a sample from deep inside the nose, reaching the back of the throat

Oropharyngeal – takes a sample from the middle part of the throat (pharynx) just beyond the mouth

Saliva samples are collected by spitting into a tube rather than using a nose or throat swab.

Blood samples are only used to test for antibodies and not to diagnose COVID-19. 

What is the difference?

The main difference between the Antigen and PCR test lies in the test processing timeframe and accuracy.

While the antigen tests are often much quicker, they are not as accurate as a PCR test, especially in the early stages of Covid-19. This test has a higher rate of producing ‘false negatives’. This is because they may have a lower sensitivity, which means they may miss some infections and may require multiple tests to ensure the virus is not present.

When looking at testing time frames, the PCR test processing usually takes longer. This is because results usually must be processed in a lab. The results are often received within 1-3 days. PCR tests are highly accurate and normally do not need to be repeated. More recently, rapid PCR tests have become available at select clinics and healthcare providers. The results from these rapid PCR tests are typically received the same day.

What To Do About False Negatives and Positives

False negatives and positives are possible.  One reason for a false negative is testing too early after being exposed and prior to developing symptoms that are able to be detected. As the tests continue to improve, a patient may look to get retested if they start or continue to show symptoms a few days after a negative test.  The occurrence of a false-positive test result is low, so even when a patient reports a false positive result, there is a good possibility that the patient has the virus.

Antigen and pcr false negatives and positives

When should I get a test?

If you have symptoms of COVID-19, even after vaccination.

If you have had close contact (within 6 feet for a total of 15 minutes or more) with someone with confirmed COVID-19, even after vaccination.

If you took part in activities that put you at higher risk for COVID-19 because you could not socially distance as needed, such as travel, attending large social or mass gatherings, or being in crowded indoor settings.

The COVID-19 tests check for the omicron, delta and other variants?

COVID-19 tests are designed and authorized to check broadly for the SARS-CoV-2 virus and not for specific variants, sometimes called SARS-CoV-2 viral mutations or genetic mutations. It is common for all viruses to change and mutate over time, resulting in different virus strains. There are no authorized COVID-19 tests that specifically report the presence of the SARS-CoV-2 omicron, delta, or other variants, in patient samples. 

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