The Difference Between Antigen vs Antibody Testing for COVID-19

Antigen vs Antibody Testing

A test is the only reliable way to know if you have COVID-19, and ideally is the first step in seeking proper medical care. If you believe that you may have been exposed to the virus, you should get tested. But what’s the difference between antigen vs antibody testing for COVID-19?


Antigen vs Antibody Testing Explained

Currently, there are three types of tests used to detect COVID-19: the antigen test, antibody test and molecular test. Both the molecular test and the antigen test can diagnose current COVID-19 infections, whereas the antibody test can check for prior infections. If you believe you may be infected, an antigen test is the fastest method currently available. This type of test is usually administered through a nasal or throat swab. If you’re wondering if you were previously exposed to COVID-19, an antibody test may be more appropriate. This test is usually administered through blood draw.


The Importance of COVID-19 Testing

Healthcare professionals and scientists use testing data to analyze COVID-19 trends. Testing data reveal important facts about infection rates, geographic areas with confirmed cases, the amount of tests administered, and other statistics. Asymptomatic individuals must self-isolate for 14 days, while symptomatic individuals should seek medical care if necessary. According to the Centers for Disease Control and Prevention (CDC), there’s still a chance that infected people without symptoms can transmit the virus. It doesn’t hurt to get tested if you suspect you have been exposed to the virus, even if you don’t have symptoms.

Testing data also facilitates contact tracing programs, which notify people who may have come into contact with someone who has tested positive. Contact tracing helps encourage people to self-isolate, reveal the extent of the virus transmission and stem further spread.


How Antigen Testing Works

Antigen testing is a new type of coronavirus screening, also known as a rapid diagnostic test. The test detects a current infection by identifying COVID-19 antigens, which are viral surface proteins that cause an immune response. The antigen test is administered by a nasal or throat swab, and you can typically expect results in hours. Antigen tests are practical for mass testing due to their speedy results and low cost.


How Accurate is Antigen Testing?

A positive antigen test result can accurately diagnose a COVID-19 infection. If the antigen test is negative, it doesn’t mean you’re in the clear. It’s possible to produce a false negative when the test sample doesn’t have enough virus proteins, especially in the early phase of infection considering that the incubation period for COVID-19 can last up to two weeks. If you were previously infected with COVID-19 and have recovered, an antigen test may not be able to detect the virus.  When an infection clears, antigens are eliminated from the body. 


How Antibody Testing Works

Also known as a serology test, an antibody test detects the presence of COVID-19 antibodies. Testing is performed using a blood sample, which is sent to a lab for analysis. The expected turnaround for test results is 24 to 48 hours. When your body detects the presence of a virus, it creates a defensive immune response by generating antibodies. Antibodies are proteins that bind to the antigens to eliminate the virus. Both antigens and antibodies have specific features that allow them to bind, like a lock and key. 

The antibody test only measures the immune response, not whether the virus is actively present. This is a key difference between antigen vs antibody testing. The antibody test detects prior history of COVID-19 exposure. Antibody tests are not considered diagnostic and cannot confirm an active infection. Antibody testing is primarily used for public health research studies. The CDC has used this testing to initiate the COVID-19 Serology Surveillance strategy, which investigates the impact of its transmission. Widespread antibody testing can reveal how prevalent the virus is within a population, including data on asymptomatic individuals.  


How Accurate is Antibody Testing?

To evaluate infection trends, it’s important to understand the limitations of antibody tests. According to the CDC, it may take one to two weeks for antibodies to be measurable. Accuracy depends on when the test is administered and the number of antibodies. Premature negative results are possible if the test is administered too soon. 

Currently, there is no scientific consensus on whether the presence of antibodies signals immunity to COVID-19. Additionally, there is not enough data demonstrating if a person who previously had COVID-19 can be re-infected. Widespread antibody testing is necessary to provide more data. Those with COVID-19 antibodies should continue to maintain health safety precautions. This includes wearing a face covering, washing your hands with soap, and maintaining a distance of at least six feet from anyone not in your household.


Molecular Testing: The Gold Standard for Detecting COVID-19

We’ve explained antigen vs antibody testing, but there’s one more test you should know about. The molecular test, also known as the RT-PCR (Reverse transcription polymerase chain reaction) test, detects genetic material from the virus and is highly accurate. Molecular tests are sent to a laboratory for analysis. When the test sample is sent to the laboratory, the tiny sample of viral genetic material is amplified, so that it can be detected. The molecular test is the most accurate test in detecting active COVID-19 infections. 

The molecular test is administered by swabbing for fluid samples in the nasal cavity using a long swab, called the nasopharyngeal swab. The swab is inserted deep into the nostril and rolled until enough sample is collected. The expected turnaround time ranges from one day to a week. 


Are COVID-19 Tests FDA Approved?

The COVID-19 antigen, antibody, and molecular tests are FDA authorized, but not FDA approved. These tests have not undergone the full process required for approval. The US Food and Drug Administration (FDA) has a comprehensive and structured process to approve new medical products.

Normally, new medical products must undergo clinical trials, which take a significant amount of time. However, the FDA’s Emergency Use Authorization (EUA) protocol has authorized COVID-19 tests for medical use. This protocol strengthens the public health response for diagnosis, treatment, and preventative care.  The COVID-19 pandemic is an urgent medical crisis that requires a special level of authorization. 


When to Get a COVID-19 Test

Health officials recommend testing if you have COVID-19 symptoms or if you have come into close contact with someone with COVID-19. Symptoms include fevers, chills, cough, shortness of breath, fatigue, muscle or body aches, headache, loss of taste or smell, sore throat, congestion, nausea and diarrhea. Please remember to consult with your doctor or healthcare provider on which test to take and to understand the results. They can share personalized insights on antigen vs antibody testing, as well as molecular testing. Your provider may also be able to provide the required medical care depending on severity of symptoms.


Where to Get Tested for COVID-19

Now that you know the difference between antigen vs antibody testing, you may want to get tested for COVID-19. The best way is to contact your healthcare provider. Some healthcare and public facilities also offer free drive-thru testing. Others require an appointment to ensure a safe environment. Be sure to call the appropriate facility before visiting. If you need to take a COVID-19 test, here are some helpful resources:


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