Public Health

Coronavirus Blood Test (antibody) vs. Swab Test (PCR) vs. Rapid COVID Test - Which is Best?

Khang T. Vuong28 Aug 2020

Jacqueline Slobin, University of Virginia Major in Global Public Health  & Alyssa Orcuilo, The City University of New York

Update August 28th 2020: There are currently two main tests for the COVID-19 virus in the United States, the PCR swab test and antibody blood test. The PCR test has recently been expanded to allow sample collection via both a nasal and a saliva sample. Read this article to find out more information about each of the tests, how they work, and their applications in this current pandemic. 

Many states have expanded their testing capacities over the past several months, making it possible for most individuals with symptoms or exposure to COVID-19 to access a test. Many health officials are recommending that you seek out a test if you are experiencing symptoms. Tests can be administered at hospitals, urgent care facilities, drive-thru centers, primary care doctors offices, and clinics. The cost of your COVID-19 cost will likely vary depending on your testing site, location, and severity of symptoms. See our latest article How Much Does Coronavirus Testing Cost With or Without Insurance for a comprehensive guide on testing costs.

There are now several companies that have released at-home COVID-19 tests that patients can perform while on a video call with a physician. These tests typically cost approximately $100 and are either taken through a saliva sample or a nasal swab. Additionally, many drive-thru testing sites are asking patients to perform the test on themselves in order to decrease contact between provider and patients.

Comparison: Key differences

The key differences between the tests.

How is the COVID Rapid Test different from the Blood and Swab tests?

What is it? 

Some urgent care facilities, testing centers, and doctors offices are offering a rapid PCR test to diagnose current infection with COVID-19. Rapid tests may be useful for individuals who need to return to work as soon as possible and cannot wait for the results of a standard PCR test.

Many online websites are advertising rapid COVID tests. Our independent research found a wide variety of tests being offered to consumers with questionable clinical accuracy. There are two main rapid tests available on the market today:

  • Rapid Swab Test: the swab test helps detect if you are currently infected. There are two FDA-authorized point-of-service machines that can carry out this test, the Abott ID Now and the Quidel Sofia 2.
    The Abott ID Now test detects the viral genetic material while the Quidel Sofia detect the viral antigen (toxin). The Abott ID Now is the only one that comes close to replicate the specificity of tests carried out in a laboratory setting (the best test to determine current infection). At this point, very few clinics have either of these machine, and neither tests are qualified for travel purposes.
  • Rapid Blood (antibody) Test: this test helps you detect past infections by measuring your body immunity to the virus. there are hundreds of finger prick rapid antibody tests available, some are approved or received emergency authorization by the FDA, but most are not. According to recent reports, the accuracy for these tests vary wildly and they are not qualfiied for travel purposes.

Timeline and Important Information 

Patients are typically able to get the results of a rapid COVID-19 test within a couple hours. Rapid tests are not available at as many locations as standard PCR tests, so make sure to call in advance to make sure this test in available.

Additionally, rapid tests may be more expensive and require and out of pocket cost. Make sure to consult with your provider regarding the accuracy of these tests. Some rapid tests have been found to be less accurate than the standard PCR test.

Which test should I get if I am traveling?

The travel restrictions and entry requirements vary between state by state and country by country, our independent research found most states require a valid COVID-19 Nucleic Acid Amplification Test (NAAT) within 72 hours of boarding from a CLIA-certified laboratory.

What does this mean in layman terms: rapid tests are not qualified. You must get a swab test sent to a lab (i.e. LabCorp, Quest Diagnostics). The procesing time is between 3-10 days, plan your travel ahead of time and get tested to avoid denied entry.

Which test should I get if I just want to know my status?

Swab Test or Antibody Lab Test (not rapid) are adequate to help you understand whether you have an active or past infection. If you don't have insurance or have a high deductible, Mira can help you get an in-office antibody test or home-delivered swab test for FREE.

What is the swab test (PCR)? And how does it work?

What is it? 

RT-PCR, or real time polymerase chain reaction, is used to detect coronavirus from a nasopharyngeal (nasal secretions) sample, also known as a nasal swab. RT-PCR is the method being used to determine the results of tests done via a testing kit. PCR COVID-19 tests are mostly being produced by Roche Diagnostics, LabCorp and Thermo Fisher Scientific.

How does it work?  

The RT-PCR technique targets a specific segment of the virus‚ genetic material to detect the presence of COVID-19 in a person. RT-PCR works by making thousands of copies of this genetic material to qualitatively assess if the virus is present. The tests only detect the virus while the person is currently infected. 

Timeline, Accuracy, and Important Information 

It is important to know that your PCR may yield a false negative result, meaning you are infected with the active coronavirus but your test result comes back negative. False negative results may be caused by taking the sample incorrectly or getting tested too soon after exposure. According to an article published by Harvard Medical School, the likelihood of receiving a false negative test result is 100% at the time of exposure.

Four days after exposure, the likelihood of getting a false negative result is 40% and after three days of symptoms, the likelihood of a false negative result is 20%. Health care professionals recommend getting tested about 7-8 days after exposure or about 3-4 days after symptom onset for the most accurate results. Therefore, if your swab test comes back negative, you cannot certainly rule out the chance of having COVID-19. Consult your provider for more details on the accuracy of the specific test they are using.

PCR tests can take up to several days (typically 3-5 days) to process; however, in some instances rapid test results can be delivered in less than an hour. While waiting for your test results, it is important to implement social distancing measures in order to mitigate the spread of the virus and decrease the number of new cases.

COVID-19 PCT test

What is the blood test (antibody)? And how does it work?

What is it? 

This test checks to see if individuals have immunity to the COVID-19 virus by looking for a specific antibody in the bloodstream. Antibodies are small proteins that are part of our immune system. They are produced to defend our body against a specific virus, for example, COVID-19.

The blood test looks for the specific antibodies that fight infection from the coronavirus. According to the Centers of Disease Control, it normally takes one to two weeks after someone becomes sick with COVID-19 for their body to make antibodies. Others may take even longer to develop antibodies to prevent against future coronavirus infection.

How does it work?  

The test checks to see if we have the antibodies for COVID-19. Antibody levels are detected through a test called ELISA, or serological enzyme-linked immunosorbent assay, and ultimately tests for the amount of antibodies in the blood for the specific virus.

In the past, it‚s been used as a diagnostic test for other diseases and viruses. The test tells us if we already had the virus, but it is not currently being used for quick detection like the swab test. Antibody tests can detect the virus even after the patient has recovered.

Timeline, Accuracy, and Important Information 

The antibody test for COVID-19 was developed a few months ago by doctors at Mount Sinai Hospital in New York. The results of antibody tests are typically delivered within 1-2 days. The test has two major implications. First, it can be used to identify potential blood donors in individuals with confirmed cases who have recovered.

Blood from COVID-19 survivors can possibly be used to treat current COVID-19 patients. Second, the antibody blood test can be used to eventually test asymptomatic individuals.

Note: testing positive for the COVID-19 antibody test means you have previously been exposed to the virus but does not necessarily confer immunity. For more details on the antibody test, what the results mean, and when to get one, see our article below.

What is the saliva test? And how does it work?

What is it? 

As of April 13, 2020 the FDA approved the use of saliva samples as a means of emergency testing for COVID-19. This test is less invasive than taking a nasopharyngeal sample and involves giving a saliva sample in a tube. Like the nasal swab, the saliva test detects active COVID-19 infection in patients who are experiencing symptoms or who may have been exposed to someone with coronavirus. The saliva test will likely be important in monitoring the number of coronavirus COVID-19 cases in the next few months.

How does it work?  

The new saliva test uses a similar protocol to that of the nasopharyngeal RT-PCR test. The test amplifies a segment of the viral genetic code to detect the presence of the virus. 

Timeline and Important Information 

This test was developed at Rutgers University and is being used by some companies for at home administration. While the saliva tests are less commonly used than the nasal swabs, they are successful in decreasing the risk of health care professionals who previously had to come into close contact with patients in order to administer a test. They may also be useful for younger people or children who are sensitive to a nasal swap.

Coronavirus saliva test

Should I get tested and where should I go? 

Testing protocols, regulations, and locations continue to vary by city during the coronavirus outbreak. If you are experiencing symptoms of COVID-19, such fever, difficulty breathing, cough, or fatigue, you should seek medical attention and inquire about getting a test. See the links below for information on testing near you: 

For a comprehensive guide to testing sites in New York City, see our article here.

If I test negative, do I still have to wear a mask?

Yes, even if you test negative for COVID-19 you should continue to wear a mask when indoors and when you are unable to maintain a distance of 6 feet from others. One negative test does not certainly rule out the chance of having COVID-19 due to some testing inaccuracies. Wearing a mask is likely to help with disease control and prevention before the development of a vaccine.

Additionally, even if you are negative, you should wear a mask to protect yourself from contracting COVID-19 from someone else. See our article Should I Wear a Mask? for more information regarding when to wear a mask, what mask to wear, and how to safely wear a mask to protect yourself and others.

Healthcare could be confusing -here are other COVID-19 resources for you:

References:

https://www.fda.gov/media/134922/download

https://www.scientificamerican.com/article/heres-how-coronavirus-tests-work-and-who-offers-them/

https://www.pacificimmunology.com/resources/antibody-introduction/what-is-an-antibody/

https://www.livescience.com/how-coronavirus-tests-work.html

https://www.the-scientist.com/news-opinion/first-saliva-test-for-covid-19-approved-for-emergency-use-by-fda-67416

https://www.health.harvard.edu/diseases-and-conditions/if-youve-been-exposed-to-the-coronavirus

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