Neutralizing Antibody

SARS-CoV-2 Neutralizing Antibody Test Related FAQs

Neutralizing Antibody FAQs

Immunity is the ability to resist a disease or an infection. Immunity to viral infection is a combined outcome of both cellular and humoral (antibody) immune responses. While cellular immune response is often difficult to measure, antibody production serves as a hallmark of humoral immune response.

Neutralizing antibody (NAb) is antibody that protect cells from pathogens. They are part of the body’s natural immune response, and their production is triggered by infections and vaccines against infections.

Neutralizing antibodies can lead to lifelong immunity to certain infections, and can be used to see if the body have developed immunity to infections after they have recovered from the infection.

The virus causing COVID-19, SARS-CoV-2, uses the Spike protein (S) to bind to the receptor on host cells to trigger cell entry and infection. S protein consists of S1 and S2 subunits, and S1 interacts with the host cells via the Receptor Binding Domain (RBD). Monoclonal antibodies to S1 protein that exhibit neutralizing activities are being developed as potential therapeutics for COVID-19. Neutralizing antibodies to the S protein are the key active ingredients of convalescent plasma used to treat severe COVID-19 patients.

Post Infection: Typically, antibodies are detectable a 2-3 weeks after infection.

Post Vaccination: Based on published vaccine trial data, 2-4 weeks following the second dose appears to be the appropriate timing for assessing immune response.

Your doctor may also wish to have a follow up testing several months later to monitor the durability of antibody levels.

Consult with your physician on the appropriate time to get tested.

An antibody test tells you if you have been infected with the virus that causes COVID-19, even if you only developed mild symptoms or were asymptomatic.

A positive result suggests that a person has been infected with COVID-19 in the past. It does NOT mean that you are immune to infection should you be infected with the virus again.

When your test is positive for the IgG antibodies for the COVID-19 virus, it means that your body is fighting off the infection or has already fought it off. Typically for most viruses, once you have developed the IgG antibodies, you are no longer contagious because the antibodies attack and inactivate the virus. But because the COVID-19 virus is new, more research is needed to determine if this is true for this specific virus.

If your test is positive for the IgM antibodies for the COVID-19 virus it typically means you were more recently infected, as IgM is typically the first antibody produced by the body to fight and control a virus, and in general stays in the blood for up to 3-8 weeks.

Regardless of the results, it is important to still remain vigilant about practicing good hygiene measures and social distancing to avoid getting infected and you should always talk to your physician if you have questions about managing your health.


Take a Neutralizing Antibody Test after your first COVID-19 vaccine dose and again after your second dose to check whether your body produced neutralizing antibodies in response to the vaccine.


Were you infected with SARS-COV-2 (COVID-19)? The Neutralizing Antibody Test can determine your immune system’s response to the infection. Experts are still learning about how long neutralizing antibodies remain in the blood after infection, and whether you are protected from reinfection in the future.

General Awareness

If you want to take a baseline test before vaccination or if you’re simply curious about your immune status, you are eligible for the test. The Neutralizing Antibody Test is available for front line workers, healthcare workers, educators, and the general public.

Potential benefits include:

  • The results, along with other information, can help your healthcare provider make informed recommendations about your care.

Potential risks include:

  • Possible discomfort or other complications that can happen during sample collection.
  • Possible incorrect test result.

No, you don’t need a referral from your doctor. We have a physician on staff who reviews and approves test registrations.

A positive test result means there has been an adaptive immune response which may be an indicator of potential protection against the virus after infection or vaccination.

If you have a positive test result, it is possible that you have or previously had COVID-19 and that you have developed an antibody response to the virus. Your healthcare provider will work with you to determine how best to care for you based on the test results along with other factors of your medical history, your symptoms, possible exposures, and geographic location of places you have recently travelled.

This test may give you a neutralizing antibody result, but you should not interpret the result to mean that having any measurement of antibodies to SARS-CoV-2 will protect you from getting infected again or help reduce the severity or duration of a future COVID-19 infection. Regardless of your test result, you should continue to follow CDC guidelines to reduce the risk of infection, including social distancing and wearing masks.

A negative test result means that neutralizing antibodies to the virus that causes COVID-19 were not found in your sample. However, it is possible for this test to give a negative result that is incorrect (false negative) in some people with COVID-19. Additionally, a negative result may occur if you are tested early in your illness and your body hasn’t had time to produce antibodies to infection. This means that you could possibly still have COVID-19 even though the test is negative.

If this is the case, your healthcare provider will consider the test result together
with all other aspects of your medical history (such as symptoms, possible exposures, and geographical location of places you have recently traveled) in deciding how to care for you. It is important that you work with your healthcare provider to help you understand the next steps you should take.

An invalid test result means there was an issue with your sample or with the test processing. We recommend that you schedule another test so we can recollect your sample.

When you come back for a re-collection, please inform the clinical staff that you are re-testing due to a previous invalid test result.

Antibody tests are playing a critical role in learning more about the virus and the fight against COVID-19. If you do test positive for antibodies, you may be a candidate to donate your plasma to be used for a patient treatment called convalescent plasma therapy that is being used by several leading healthcare institutions to help patients with COVID-19 who are sick or critically ill to recover.

Each antibody can bind an epitope (small region of the antigen in contact with the antibody binding site). Only some anti-viral antibodies bind to the regions in the viral antigens that are involved in binding to cellular receptors and are crucial for the infection process. If a given antibody recognizes an epitope outside these regions involved in the infection, it would not inhibit the infection. On the other hand, a neutralizing antibody binds to (or near to) the region in the virus that initiates cell infection, and can thus block this process, being protective for the host.

Neutralizing Antibody


  • SARS-CoV-2 has a biological key, called a spike protein that allows it to bind to receptors on the cell membrane and unlock the door to human cells.
  • Once inside of cells, the virus replicates and causes infection such as COVID-19.
  • The immune system produces neutralizing antibodies which bind to the viral spike protein and block its ability to function as a key.
  • Neutralized SARS-CoV-2 can no longer enter human cells or cause infection.
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