What are antibody tests for #covid19, and why are they useful?

These are going to help reopen America, and improve future mitigation and containment efforts supporting public safety. <thread>

When your body is infected with SARS-CoV-2, two things happen:
- The virus replicates.
- Your body fights the virus, creating antibodies.

The nasopharyngeal swabs and RT-PCR tests detect shed virus. We can also detect the response to the virus in blood, however.

The most important antibody isotypes relating to SARS-CoV-2 infection are IgG and IgM.
- IgM forms the initial antibody response, and is evident early in the disease.
- IgG predominates later in the disease process, remaining detectable in blood after the disease resolution.

When do we use these tests?
- A nasopharyngeal swab can be used in acute infection to establish the presence of virus.
- This test is limited by the quality of the sample, misses about 10-20% of infections, and only detects active infection.

The blood serologies can be used in different ways, but require interpretation. Finding IgM in the blood can help establish active or recent infection, but has sensitivity limitations, particularly early in acute infection.

Finding IgG in the blood, however, well-establishes prior infection with SARS-CoV-2. This is profoundly important, as these individuals are thought to be at lower risk for re-infection, transmission, and contribute to "herd immunity".

In these early stages here in the U.S., the number of infected vastly exceeds the number tested for acute infection. These #covid19 serology tests will be invaluable in helping individuals and communities determine risk for returning to normal life.

In acute infection, both blood serology and NP swabs may play roles in maximizing sensitivity for #covid19. Improving sensitivity has implications for protecting patients and healthcare workers, along with conserving protective equipment.

For now, these tests are still being validated, as well as algorithms tailored to local needs. #stayhomesavelives!