Deciding on antigen vs. antibody tests when choosing a COVID-19 test is easier when the definitions and their function are clear. These tests represent different ways you can check for SARS-CoV-2, the virus that causesCOVID-19.
An antigen test looks for an active infection, based on the presence of a virus, allergen, or other foreign antigen that sparks an immune response. An antibody test looks for signs of a past infection, based on the body’s production of antibodies as an immune response to exposure.
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COVID-19 Antigen Tests
Anantigenis any foreign or toxic substance your immune system knows does not belong in your body. Antigens can beviruses,allergens, or even chemicals that prompt an immune response to fight illness or infection.
Antigens are required to trigger the process of producing antibodies.Since the presence of antigens is the earliest evidence that a virus has entered your body, antigen testing helps detect a current viral infection. They can be used to diagnose respiratory infections like COVID-19,influenza, and respiratory syncytial virus (RSV).
Antigen tests are usually:
Rapid antigen tests are most accurate if you develop symptoms of a COVID-19 infection, or at least five days after a known exposure to someone who was sick.
Antigen tests are not typically as sensitive as real-time reverse transcription polymerase chain reaction (RT-PCR) and other nucleic acid amplification tests (NAATs) that identify genetic pieces of a virus. Still, they help make quick test results widely accessible.
What to Do With a Positive Antigen TestA positive antigen test result indicates a current infection. To reduce the chances of spreading COVID-19, the Centers for Disease Control and Prevention (CDC) recommends that you:Isolate at home until you’ve been fever-free for 24 hours(without taking fever-reducing medication) AND your symptoms are mild and improving.Take additional precautions for five days following isolation, such as wearing a well-fitting mask, keeping a distance from others, and washing your hands often.If you test positive but have no symptoms, you should take added precautions for the next five days. For negative results, a total of two negative antigen tests (or three, with no symptoms) should be done 48 hours apart. A single NAAT test also can be used to confirm results.
What to Do With a Positive Antigen Test
A positive antigen test result indicates a current infection. To reduce the chances of spreading COVID-19, the Centers for Disease Control and Prevention (CDC) recommends that you:Isolate at home until you’ve been fever-free for 24 hours(without taking fever-reducing medication) AND your symptoms are mild and improving.Take additional precautions for five days following isolation, such as wearing a well-fitting mask, keeping a distance from others, and washing your hands often.If you test positive but have no symptoms, you should take added precautions for the next five days. For negative results, a total of two negative antigen tests (or three, with no symptoms) should be done 48 hours apart. A single NAAT test also can be used to confirm results.
A positive antigen test result indicates a current infection. To reduce the chances of spreading COVID-19, the Centers for Disease Control and Prevention (CDC) recommends that you:
If you test positive but have no symptoms, you should take added precautions for the next five days. For negative results, a total of two negative antigen tests (or three, with no symptoms) should be done 48 hours apart. A single NAAT test also can be used to confirm results.
COVID-19 Antibody Tests
An antibody is a protein your immune system produces after sensing a foreign substance in your body. When your immune system detects a virus, bacterium, allergen, or another substance, it creates proteins (antibodies) to neutralize similar substances the next time you encounter them.
Antibody testingdetermines whether your body has an immune response to an antigen. The purpose of antibody testing in the case of COVID-19 is to:
Although you can purchase antibody tests for home use, you should not use them to test for an active infection. Even if you are trying to test for a previous infection, the results of an antibody test may not be accurate until one to three weeks after you first became infected.
Antibody testing is generally more useful for public health purposes than for making a clinical diagnosis. Testing information can be used for disease surveillance and tohelp tailor vaccines or boostersto protect against the most current variants.
Antigens and Antibodies Work TogetherAntigens allow your body to create a defense against future invaders. Antibodies circulate in your body once created to identify, attack, and destroy the same type of antigens if they enter the body again.Once your body recognizes a particular virus or bacterium and produces an antibody to fight it, you will be less vulnerable to infection from that same virus or bacterium again.
Antigens and Antibodies Work Together
Antigens allow your body to create a defense against future invaders. Antibodies circulate in your body once created to identify, attack, and destroy the same type of antigens if they enter the body again.Once your body recognizes a particular virus or bacterium and produces an antibody to fight it, you will be less vulnerable to infection from that same virus or bacterium again.
Prevention
You can protect yourself and your loved ones from a COVID-19 infection in several ways.Vaccines and updated boostersare available and can offer you robust protection. Public health experts also recommend the following:
Summary
Antigen tests can detect a current COVID-19 infection and are available in labs, clinics, healthcare provider offices, or as at-home tests. Antibody tests won’t identify an active infection, but they may help determine if your body has created antibodies against SARS-CoV-2 from a previous infection or vaccination.
8 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Centers for Disease Control and Prevention.COVID-19 testing: What you need to know.MedlinePlus.Antigen.U.S. Food and Drug Administration.At-home COVID-19 antigen tests-Take steps to reduce your risk of false negative results: FDA Safety Communication.Centers for Disease Control and Prevention.Preventing spread of respiratory viruses when you’re sick.National Institutes of Health.Antibody.Centers for Disease Control and Prevention.Interim guidelines for COVID-19 antibody testing.Food and Drug Administration.Antibody (serology) testing for COVID-19: Information for patients and consumers.Centers for Disease Control and Prevention.How to protect yourself and others.
8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Centers for Disease Control and Prevention.COVID-19 testing: What you need to know.MedlinePlus.Antigen.U.S. Food and Drug Administration.At-home COVID-19 antigen tests-Take steps to reduce your risk of false negative results: FDA Safety Communication.Centers for Disease Control and Prevention.Preventing spread of respiratory viruses when you’re sick.National Institutes of Health.Antibody.Centers for Disease Control and Prevention.Interim guidelines for COVID-19 antibody testing.Food and Drug Administration.Antibody (serology) testing for COVID-19: Information for patients and consumers.Centers for Disease Control and Prevention.How to protect yourself and others.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Centers for Disease Control and Prevention.COVID-19 testing: What you need to know.MedlinePlus.Antigen.U.S. Food and Drug Administration.At-home COVID-19 antigen tests-Take steps to reduce your risk of false negative results: FDA Safety Communication.Centers for Disease Control and Prevention.Preventing spread of respiratory viruses when you’re sick.National Institutes of Health.Antibody.Centers for Disease Control and Prevention.Interim guidelines for COVID-19 antibody testing.Food and Drug Administration.Antibody (serology) testing for COVID-19: Information for patients and consumers.Centers for Disease Control and Prevention.How to protect yourself and others.
Centers for Disease Control and Prevention.COVID-19 testing: What you need to know.
MedlinePlus.Antigen.
U.S. Food and Drug Administration.At-home COVID-19 antigen tests-Take steps to reduce your risk of false negative results: FDA Safety Communication.
Centers for Disease Control and Prevention.Preventing spread of respiratory viruses when you’re sick.
National Institutes of Health.Antibody.
Centers for Disease Control and Prevention.Interim guidelines for COVID-19 antibody testing.
Food and Drug Administration.Antibody (serology) testing for COVID-19: Information for patients and consumers.
Centers for Disease Control and Prevention.How to protect yourself and others.
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