Antibody Testing

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Antibody Testing

The COVID-19 antibody test determines whether someone previously had the virus by detecting the presence of antibodies. It does not check for the virus itself—only a viral test is used to diagnose someone who is currently sick. Instead, it detects the presence of antibodies that shows the immune system was activated to respond to the infection.

It can take 1-3 weeks after infection for enough antibodies to build up in the body and be detected by the antibody test. That’s why it is important not to perform the test too early in the course of the infection. In fact, it is typically done after someone has fully recovered.

Unlike the viral test that uses a swab to check respiratory samples typically taken from inside the nose, the antibody test is a blood test performed by a healthcare professional who takes a sample by drawing blood from a vein in the arm. When someone tests positive for COVID-19 antibodies, it indicates they likely were infected with the novel coronavirus sometime in the past.

While the presence of antibodies often indicates immunity, the World Health Organization cautions that there’s a lack of evidence on whether having COVID-19 antibodies signifies that someone is protected against reinfection with the virus. The level of immunity and how long immunity lasts are not yet known. That is why people who have recovered from COVID-19 should still take precautions and practice physical distancing, facial covering and hand hygiene recommendations.

Currently, Sonoma County is conducting antibody testing only for First Responders (paramedics, EMTs, firefighters, law enforcement) and Healthcare Workers at high risk for exposure to COVID-19. First Responders and Healthcare Workers should call (707) 565-4667 to schedule an appointment for an antibody test.

Members of the public who are identified as cases or contacts—such as family/household members and close contacts of people who previously tested positive for the virus—are being contacted by Public Health Disease Control representatives to schedule an antibody test.

There is no charge for antibody testing. Test results are delivered by phone or email within three weeks.

List of FAQs

No COVID-19 antibody test is 100% accurate. It’s possible to test negative yet actually have been infected (false-negative result).

While there have been many antibody tests with questionable accuracy on the market since the start of the COVID-19 pandemic, the U.S. Food and Drug Administration (FDA) has removed the majority of them from circulation. The test used in Sonoma County has a high-degree of accuracy–meaning that nearly 98% of those who test positive for antibodies had COVID-19 and nearly 100% of those who test negative did not have the virus.

Antibody testing is an important way to learn more about this novel coronavirus–how it spreads in the community and the way in which it impacts people differently. For example, many people who are infected with COVID-19 never experienced symptoms; they nonetheless may have been contagious and unknowingly spread the virus to others. This information will help us conduct contact tracing and reach out to people who may have had close contact with a person who previously was infected, monitor them for symptoms and get them the care they need while protecting others from exposure. In addition, someone may have tested positive for COVID-19, but never developed antibodies.

The more we learn about the virus, the more we can share and apply this knowledge to reduce the risk of its spread by adopting healthy behaviors such as social distancing, facial covering and hand hygiene until an effective treatment and vaccine are readily available to the public.

People who have recovered from COVID-19 may be eligible to donate plasma, which is a component of blood. This plasma could be used to treat others with severe disease and boost their ability to fight the virus. Doctors call this “convalescent” plasma.

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