What Is the COVID-19 Antigen Test? How It Works

What is the COVID-19 antigen test? Learn what the rapid antigen test is used for, how it works, and what the pros and cons are

COVID-19 antigen testing is a new diagnostic method for detecting coronavirus that received emergency use authorization by the U.S. Food and Drug Administration (FDA). 

The rapid COVID-19 antigen test detects the presence of SARS-CoV-2 virus proteins in the sample, allowing early detection of the infection.

How does the COVID-19 antigen test work?

An antigen is a substance (protein) that causes the immune system to produce antibodies and trigger an immune response. In the case of COVID-19, spike proteins are found on the surface of SARS-CoV-2 virus. Therefore, the antigen test detects these proteins or genetic material of the SARS-CoV-2 virus. 

The rapid antigen test should be performed during the initial days after the onset of symptoms and for asymptomatic people who have had recent direct contact with a COVID-19-positive person.

How to use an at-home COVID-19 antigen test

The COVID-19 antigen test is affordable and may allow people to test themselves for COVID-19 rather than relying on getting tested at a screening center. The test includes all the necessary material for its use in nasopharyngeal samples:

• Collect the mucosa sample through the nasal cavity with the help of a sterile swab. Then carefully remove the swab.
• Insert the swab into the extraction tube and press in the area indicated by arrows.
• Rotate the swab according to the instructions for use and remove it from the extraction tube.
• Place the cap on the tube nozzle and apply the extracted sample to the well of the cassette according to the instructions in the manual.
• Read the test result in the time indicated in the manual (usually 15 to 30 minutes).

The antigen test is read as either positive (with test and control lines visible), negative (only control line is visible) or invalid (only test line appears or no line appears). Newer devices have digital immunoassays that display the result as positive, negative, or invalid rather than relying on the operator to read the results off the strip.

The World Health Organization currently states that rapid antigen detection tests (RADTs) should only be used if reverse transcription polymerase chain reaction (RT-PCR) is not available, and it must be proven to have ≥90% sensitivity and 99% specificity.

What are the pros and cons of the COVID-19 antigen test?

Pros

• Speed: 
  • One of the benefits of antigen testing is the high speed of testing compared with the standard reverse transcription polymerase chain reaction (RT-PCR).
  • Once the sample is added to the testing strip, it takes about 10 to 15 minutes for the results to appear. These procedures may differ from test kit to test kit.
• Cost:
  • Antigen testing is less expensive compared with other tests.
• Convenience:
  • People can test themselves comfortably in their homes and do not require personal protective equipment.
  • In fact, antigen testing kits do not require extensive laboratory training because most critical steps are automated in a single device.

Cons

• Accuracy:
  • Results are unfortunately not as sensitive, although antigen testing technology continues to improve..
  • If the test result is negative and clinical symptoms persist, additional testing using other clinical methods is recommended. A negative result does not at any time preclude the possibility of SARS-COV-2 infection.
• False positive results:
  • Positive antigen tests are considered much more accurate, but they still can produce false positives. 
  • The concern is that false positives could be caused by the presence of other viruses, improper collection techniques, or other substances produced by the body during infection that interfere with the results. 

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What other tests are used to detect COVID-19?

Molecular/polymerase chain reaction (PCR) tests

• Reverse transcription polymerase chain reaction (RT-PCR) is the gold standard of diagnostic testing for COVID-19.
• A molecular test is usually performed using a technique known as PCR that works by rapidly making millions to billions of copies of viral-related deoxyribonucleic acid (DNA).
• If there are even small amounts of this genetic material in the sample, it will be detected. Thus, molecular/PCR tests are very sensitive, and they are very specific.
• A positive test is almost never wrong in determining that SARS-CoV-2 is present.
• Tests can be done on samples taken by nasal or throat swabs and even by saliva.

Antibody tests

• An antibody test looks for the body's response to SARS-CoV-2 virus that causes COVID-19.
• The antibody test should not be used to diagnose the virus. It is a blood test that is good at determining if you had the disease but not good for determining if you have the disease.
• Positive antibody tests are currently used for epidemiological surveys.