When a person is exposed to an infectious agent, the immune system recognizes antigens of that pathogen as a foreign body. The immune system targets these antigens by making antibodies against them.
Generally, IgM and IgA antibodies levels rise after three to seven days of viral infection and then gradually decline. Meanwhile, IgG antibodies begin to increase after 12-17 days and then persist for a relatively long time.
Antibody levels are useful to record exposure and potential immunity, according to an analysis prepared with significant input from Ernst J. Schaefer, MD, Professor of Medicine at Tufts University School of Medicine and the Chief Medical Officer & Laboratory Director at Boston Heart Diagnostics.
These test in documenting antibody levels is called the serological test. But take note, serological or antibody tests do not detect the virus itself, but only the antibodies that the immune system has made. Inaccurately diagnosing COVId-19, doctors and specialists use RT-PCR tests.
Inaccurate Coronavirus Antibody Tests
The new review that was released on Wednesday reveals a sad truth about the state of antibody tests meant to determine whether someone already had COVID-19. It suggests that these coronavirus antibody tests range widely in accuracy from one manufacturer to another. These tests quickly return results to the doctors faring so badly that they should have never been used at all for now.
These antibody or serological tests are designed to tell if someone had the virus in the past, even without feeling sick at the time. However, in reality, it has been more complicated than that.
In March and April, the first COVID-19 antibody tests became available in the US, although other countries have also developed their versions earlier. Many of these tests were initially distributed globally were cleared for use with little outside validation of their accuracy by relevant health agencies such as those in the US.
Eventually, FDA has placed stricter restrictions on the clearance and approval of these tests and now maintains a list that has been removed from the market.
The researchers involved in this new review, published in BMJ, examined 40 studies evaluating the accuracy of antibody tests for COVID-19 developed from countries worldwide. They tried to measure the sensitivity and specificity of these tests.
Moreover, they pooled together results categorizing them by the types of tests being studied in China, the US, Italy, and Japan.
Overall, the studies were not necessarily of high quality, and half had not even gone through peer review at the time. Additionally, nearly all of the tests were considered a high risk of bias in selecting patients for the study and how they were interpreted.
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Furthermore, the risk of false negatives varied between tests ranging from 66% to over 97.8%. Its specificity, also range from 96.6% to 99.7%. Of these tests studied, it was rapid testing that fared the worst of all.
That means if a city with 10% coronavirus patients, these rapid tests would wrongly identify 31 false positives out of every 1,000 people tested, along with 34 false-negative results.
Other Concerns About Using Rapid Antibody Tests
Recent evidence suggests that there are other concerns of using antibody tests in confirming immunity from the virus. For instance, a new study identified some antibodies that may fade away from COVID-19 survivors just within a few months, especially those asymptomatic patients.
The authors of the review wrote that there must be a concerted effort in validating the accuracy of antibody tests before conducting extensive testing to avoid false positives and false negatives.
