Touted as an exciting breakthrough in testing, the new antibody test for COVID-19, created by Chembio Diagnostic Systems, looks like it may not provide the answers that we’ve been waiting for. There are some serious problems with this type of testing, and it’s reliability for determining who might be immune to SARS-CoV2 seems to fall short of what has been marketed as simple finger prick that will give those immune the green light to go back to work. Unfortunately, it doesn’t appear to be that simple. For one, the test seems to be reasonably reactive to other species of coronavirus, which would be a significant complication considering that there are many types of human coronaviruses that cause the common cold and other mild infections. According to the test’s instructions, “false-positive results for IgM and IgG antibodies may occur due to cross-reactivity from pre-existing antibodies or other possible causes.” and that “false-positive results due to cross-reactivity with antibodies to other coronaviruses, (e.g., HKU1, 229E, NL63, OC43) can occur.”
In the cross-reactivity test, one sample was tested for Human coronavirus 229E and showed a positive result (100%), and 1 out of five tests for Human Coronavirus HKU1 tested positive (20%). These viruses are causes of the common cold, and many people are likely to possess antibodies to these viruses.
The SARS-CoV2 antibody test also has a high margin for false negatives during the first few weeks of illness. The development of an antibody response to SARS-CoV2 can take up to two weeks or more after the onset of symptoms. In the testing phases of this antibody test, the results only proved to be reliable after the patient’s 14-day mark. The test insert states: “A negative result does not exclude possible infection with COVID-19, particularly in those who have been in contact with the virus, and should not be used as the sole basis for treatment, patient management decisions, or to rule out active infection.”
The test can also present a false negative if there is not a dense enough concentration of antibodies in the sample, which can happen in the early stages of infection and throughout the course of the infection for people with weak immune systems. The test will also pick up a false negative if the virus has mutated at all from the strain used in designing the test. We know that the virus has mutated several times already, and it is unclear whether or not this test takes that into account. If not, the instances of false negatives could be much higher.
“A negative or non-reactive result can occur if the quantity of antibodies for the SARS-CoV-2 virus present in the specimen is below the detection limit of the assay, or the virus has undergone minor amino acid mutation(s) in the epitope recognized by the antibody utilized in the test.”
With all of these issues in question, one has to wonder, what is the point of this test? If it is not able to accurately determine a positive or negative result until several weeks following the onset of symptoms, and taking into account that an infected patient can go 1-4 weeks before showing symptoms, this antibody test is useless for determining acute infection.
Furthermore, this test does not indicate immunity. This test insert includes the disclaimer: “The DPP COVID-19 IgM/IgG System is limited to the qualitative detection of antibodies specific for the SARS-CoV-2 virus. The intensity of the test line does not necessarily correlate to SARS-CoV-2 antibody titer in the specimen” and that “at this time, it is unknown for how long IgM or IgG antibodies may persist following infection.”
Our source at AZ News thinks that these test kits are purely motivated by capitalism versus accuracy and that they will result in a waste of time and money. The question is, why is this antibody test being heralded as the answer to restarting our society. Yet, at best, it is vulnerable to the same inaccuracies of similar tests of it’s kind. At worst, it is the first glimpse at the medical testing industry’s cash grab following the relaxed testing standards of the FDA in February that will now allow body-fluid tests to proceed to market without full agency review and approval.