Updated July 16, 2020

FMI Recommendations for Testing:
  • Molecular (or viral) testing should be used for diagnosis of individuals who are at risk for COVID-19 or who have symptoms of COVID-19. All testing should be done in collaboration with physicians and/or health departments.

  • Serological testing may be used for public health purposes to evaluate past exposure to COVID-19. Serological testing should not to be used for diagnostic purposes and ideally should not be identified with individual data.

  • Any molecular or serological test used should be approved by the FDA and the sensitivity and accuracy of the tests should be known and taken into consideration when selecting tests and analyzing results.

What are the tests for COVID-19 and SARS-CoV-2?

There are two types of tests currently available for COVID-19. The first is a molecular or viral test which detects the actual virus in the respiratory tract, specifically the nasal cavity. A swab is inserted into the nasal cavity to collect a sample of mucus or respiratory fluid. The sample is then analyzed in a laboratory or rapid kit for the genetic material of the virus or the molecules that make up the virus. The second type of test is a serological test that detects antibodies for SARS-CoV-2 in the blood or serum. A blood sample is taken from a person and the blood is analyzed to determine if the person has had an immune response to the COVID-19 virus in the past. If someone tests positive for the serology test, it means that they have been exposed to the virus at some point in time and their immune system produced antibodies. Sustained immunity is unknown at this point.

The two types of tests are very different, are used for different purposes, sample different systems (respiratory and immune) and tell us different things (active infection and possible past infection).

How does the serology or antibody test work?

The serology or antibody test, measures the amount of antibodies present in the blood when the body is responding to a specific infection, like COVID-19. This means the test detects the body's immune response to the infection caused by the virus rather than detecting the virus itself. In the early days of an infection when the body's immune response is still building, antibodies may not be detected. This limits the test's effectiveness for diagnosing COVID-19 and why it should not be used as the sole basis to diagnose COVID-19.

In response to an infection, such as COVID-19, the body develops an overall immune response to fight the infection. One component of the immune system's response is development of antibodies that attach to the virus and help eliminate it. The body's initial immune reaction produces general antibodies that attack many infections, called Immunoglobulin M (IgM) antibodies. IgM antibodies indicate an active or recent infection. Because it takes time for the body to make IgM antibodies in response to SARS-CoV-2, their absence does not mean that someone is not infected. A test for IgM antibodies may give a false negative result in a patient with SARS-CoV-2, particularly early in infection. A patient may have a negative result early in infection even when they are symptomatic or asymptomatic but actively shedding the virus. Since IgM antibodies may not develop early or at all in infected patients, this type of antibody test is not used to rule out SARS-CoV-2 in an individual.

Over time, the body develops a second type of antibody in response to the infection that is more specific to the virus, called Immunoglobulin G (IgG) antibodies. Most antibody tests detect IgG antibodies. On average, IgG antibodies take about 4 weeks to develop, but the time to develop may vary substantially, and there is still a lot we do not know about SARS-COV-2. Since IgG antibodies generally do not develop until several weeks after infection, this type of antibody test, even though it is more specific to SARS-CoV-2, is not used to rule-out SARS-CoV-2 infection in an individual.

We also do not know how long IgM or IgG antibodies to SARS-CoV-2 will remain present in the body after the infection has cleared. Therefore, we do not know if people will be immune to COVID-19 if they have previously had the virus.

If the serology test is not for diagnosing COVID-19, what is it good for?

The serology test is helpful for public health officials to utilize for communities or special populations to evaluate exposure to the virus. It has been reported that exposure has been much broader than diagnosed cases. Public health professionals are very interested in evaluating and researching exposure to the virus and asymptomatic exposure to COVID-19.

As an employer, may I test employees for COVID-19 as a screening tool?

Yes, on April 23, 2020, the Equal Employment Opportunity Commission (EEOC) clarified in guidance that an employer may administer a COVID-19 test (a test to detect the presence of the COVID-19 virus) before permitting an employee to enter the workplace. In the guidance, EEOC explains that the Americans with Disabilities Act (ADA) requires that any mandatory medical test of employees be "job related and consistent with business necessity." Applying this standard to the current circumstances of the COVID-19 pandemic, employers may take steps to determine if employees entering the workplace have COVID-19 because an individual with the virus will pose a direct threat to the health of others.

On June 17, the EEOC updated their Q&A guidance page to include a section concerning antibody testing. Based on the CDC’s interim guidelines for antibody testing, the EEOC determined that employers cannot require workers to take such a test in order to return to work. These particular procedures attempt to determine whether an individual previously had the coronavirus by examining whether they retain antibodies in their bloodstream. Since these do not establish whether a person actively has the coronavirus, the EEOC felt that such a requirement would be a violation of the Americans with Disabilities Act. Note: employers can still require regular diagnostic testing of employees if intended to determine whether an individual actively has the virus or not.

If I choose to administer a test, what test should I use?

In the April 23, 2020 guidance, the EEOC states that employers should ensure that the tests used are accurate and reliable. For example, employers may review guidance from the U.S. Food and Drug Administration about what may or may not be considered safe and accurate testing, as well as guidance from CDC or other public health authorities, and check for updates. EEOC further cautions that employers may wish to consider the incidence of false-positives or false-negatives associated with a particular test. Finally, note that accurate testing only reveals if the virus is currently present; a negative test does not mean the employee will not acquire the virus later.

Based on guidance from medical and public health authorities, EEOC states that employers should still require - to the greatest extent possible - that employees observe infection control practices (such as social distancing, regular handwashing, and other measures) in the workplace to prevent transmission of COVID-19. 

As an employer, when should I test employees for COVID-19?

If there is an outbreak or a high level of community transmission of COVID-19, the molecular (or viral) test for COVID-19 could be used to test employees in collaboration with the health department and/or a health care provider. Procedures should be in place for managing personal information, communications and dealing with positive employees and absences due to positive employees.

There are many tests available and I have been contacted by many test providers. What test should be used for COVID-19?

The FDA approves tests for COVID-19 as medical devices. If your employees are tested for COVID-19 with the molecular or the serological tests, please make sure that any tests used are approved by the FDA. Tests also have different sensitivities and accuracies. You need to know the sensitivity level of the test and the accuracy level of the test. For example, one of the most popular tests in use has a 15% false negative rate. This should be taken into consideration in decision making with symptomatic employees post testing since 15% could still be positive for COVID-19. All testing should be done in collaboration with medical professionals.

Additional Resources:


CDC, “Testing for COVID-19; Accessed on April 23, 2020

FDA, “FAQs on Testing for SARS-CoV-2; Accessed April 23, 2020, May 6, 2020

FDA, “Immediately in Effect Guidance for Clinical Laboratories, Commercial Manufacturers, and Food and Drug Administration Staff: Policy for Diagnostic Tests for Coronavirus Disease-2019 during the Public Health Emergency”Accessed on April 23, 2020

FDA, “Products approved by the FDA under the Emergency Use Authorization (EUA); Accessed May 6, 2020

NCBI, “Features, Evaluation and Treatment Coronavirus (COVID-19); Accessed on April 23, 2020