New test can detect presence of COVID-19 antibodies from small saliva samples

The new saliva-based test is seen as potential alternative to blood-sample antibody tests for research and clinical use.

Currently, COVID-19 antibody tests are conducted either through a finger prick or blood drawn from your arm. The blood is then inspected for the presence of IgM and IgG antibodies, which are produced by the immune system to provide protection against SARS-CoV-2, the virus that causes COVID-19. While IgM antibodies develop early on in an infection, IgG antibodies are more likely to show up later and usually remain for months or years. Soon, this painful test may be replaced by a new saliva-based test.

Developed by a team at Johns Hopkins Bloomberg School of Public Health, the new test can accurately detect the presence of antibodies to SARS-CoV-2 from small samples of saliva. The results of the test can be obtained in a matter of hours, the researchers said.

The new saliva-based test is seen as potential alternative to blood-sample antibody tests for research and clinical use.

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How saliva testworks?

In the study, Bloomberg School researchers found that their test could detect antibodies to several SARS-CoV-2 antigens in saliva samples from all 24 participants who had confirmed SARS-CoV-2 exposure and whose symptoms had begun more than two weeks prior to the test.

The test also showed negative results for most saliva samples that had been collected from people prior to the COVID-19 pandemic. Saliva-based testing seemed to be particularly specific to IgG antibodies to SARS-CoV-2, as the scientists found negative results for it in all 134 of the pre-COVID-19 samples. This result appeared to be just as accurate as blood-based serological testing.

Further, their experiments showed that people who become infected with the novel coronavirus develop detectable antibodies in saliva at roughly the same time as they do in blood. IgG antibodies typically elevate around day 10 after the onset of the COVID-19 symptoms, but they may also spill over from the blood into saliva, according to the researchers.

The findings of the study appeared online in the Journal of Clinical Microbiology.

Antibody test vs PCR test

Polymerise chain reaction (PCR) and antibody testing are the two most common methods used to screen people for COVID-19 infection.

The PCR tests is used to detect the genetic material of the virus (the RNA) from the nasal and throat swab samples, rather than the presence of the antibodies. This test can tell whether or not someone has the virus very early on even before symptoms of the disease are present and antibodies are formed.

PCR tests involve several stages between sampling and analysis, and this increases the chances of errors. Another disadvantage of this test is that it may miss those patients who have cleared virus and recovered from disease.

An antibody or serologic test can tell who's been infected as well as who should be immune to the virus. But it may not be able to identify who is infected as the antibodies are usually produced after a week or two of the infection. By then the virus may have been cleared from the system.

The PCR test helps you detect current active COVID-19 infection, and antibody test can detect past infections.

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