ELISA or “enzyme-linked immunoassay,” a shorter term for serological enzyme-linked immunosorbent assay, is currently the talk of the town in the medical field. It’s a screening test that can determine whether a person has or had or was infected with SARS-CoV-2, the virus that causes COVID-19.
In addition to that, the ELISA test is an antibody test. Recent studies claimed that people who have recovered from COVID-19 carry antibodies to the virus. According to the World Health Organization, antibody-mediated immunity is a potential treatment for COVID-19.
ELISA blood test vs. PCR swab test
The ELISA test is primarily designed to detect immunoglobulins or antibodies against the SARS-CoV-2 (virus) that causes COVID-19 (disease). In general, the ELISA test can detect immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies.
The ELISA test has been brought into play after finding out that the polymerase chain reaction (PCR) testing results (the current nasal swab tests used as a frontline DNA/genetic test for SARS-CoV-2) has been labeled as “presumptive evidence” of COVID-19.
Current research claimed that 25% of the PCR nasal samples are false negatives. Factors like improper collection, handling, or storage can be among the reasons for this situation. There’s a big chance that laboratory errors may happen, as well.
Moreover, PCR testing doesn’t give information about a person’s immunity to infection and doesn’t test for antibodies to the virus. In other words, the swab tests cannot lead to the cure of COVID-19. Conversely, recent studies have also discovered that antigens and antibodies (ELISA) are more stable compared to RNA (PCR), which reduces the false-negative rate.
Researchers claimed that the ELISA test could deduce whether one’s immune system had made contact with SARS-CoV-2, even months before. This test’s results can supply more relevant information to the convalescent plasma testing, an experimental treatment for COVID-19.
What does a positive result on the ELISA test mean?
A positive result on the ELISA test means IgG and IgM antibodies are detected in one’s system. The detection of these antibodies indicates past infection of SARS-CoV-2.
The detection of IgM, with or without IgG, can indicate that a person had just been infected recently. Meaning, this person can be infectious to others. If this is the case, this person should confirm it with a swab test.
Alternatively, the detection of IgG, without IgM, can indicate that a person had been infected weeks or months ago, which may mean that he or she is no longer infectious. Also, IgG may suggest that a person has immunity against COVID-19 or not.
That said, it’s noteworthy that a positive result may still be a false positive. This, however, depends on the manufacturers of the IgM and IgG test kits. Some companies claimed to have a 99% false-negative rate after two weeks, while others have lower rates.
What does a negative ELISA test mean?
A negative result on the ELISA test means there were no antibodies to the SARS-CoV-2 that had been detected. Still and all, chances of false negatives may still take place.
A person could still have COVID-19, although he or she tested negative, too. This can potentially happen if a person undergoes a test a bit earlier, usually during the time when the body hasn’t generated the antibodies against SARS-CoV-2 yet. If symptoms occur despite negative ELISA test results, it’s advised to take a test again, depending on what your health care provider suggests.
False Negatives and False Positives
The World Health Organization is now supporting countries that are now undergoing mass testing for SARS-CoV-2 antibodies. Due to the kits’ high costs, other countries are only testing in a specific group, such as close contacts of infected cases, health practitioners, frontliners, or within households. However, individuals can purchase IgM IgG kits for Coronavirus online.
Further, there are two main ways inaccurate laboratory tests may falsely label a person:
1. Categorizing infected people as “negative.”
2. Categorizing people with no infection as “positive.”
Both laboratory errors have negative implications on control efforts. Categorizing infected people as “negative” allows the infected people to spread the virus continually. On the other hand, categorizing people with no infection as “positive” means exposing them to other infected people, infecting the former in the long run.
Based on the ELISA results, a person’s medical history and past actions, professional health care providers would work with you in determining the best care you should take or personally do.
The ELISA test only determines whether a person has been exposed to SARS-CoV-2 at present or in the past. It doesn’t confirm the presence of the said virus in a person’s system. Also, IgG detection only suggests a person’s possible immunity to the virus, but “how much immunity” is still unknown.
Since it’s only a screening test, immunoglobulin tests like ELISA tests should be paired best with a genetic-based test like PCR, according to studies. Doing the two tests in tandem would be a gold standard for COVID-19 diagnosis, which can potentially lead to the pandemic’s treatment.