India Cancels Chinese Antibody Kits: Can You Trust Rapid Tests?
The ICMR asked the states and UTs to stop using the rapid antibody COVID-19 testing kits procured from China
The Indian Council of Medical Research on Monday, 28 April asked the states and union territories to stop using the rapid antibody COVID-19 testing kits procured from China due to "wide variation" in their performance even as the government said not a single rupee will be lost as payments were not made to the Chinese suppliers of the equipment.
India had procured around five lakh rapid antibody test kits from the two Chinese firms, Guongzhou Wondfo Biotech and Livzon Diagnostics, and they were distributed to several states reporting rising cases of the coronavirus infection.
With new questions and confusion arising about the quality and efficacy of antibody tests, we explore how reliable are these tests and why are they being touted by many including the ICMR against COVID-19?
Notably, thus far, ICMR has only canceled the faulty kits procured from China. On Monday, it also released a new guideline for the use of these tests.
FIT spoke to Dr Shahid Jameel who is a Virologist & CEO of Wellcome Trust DBT India Alliance to understand what antibody tests are.
He explains, "When you get infected by a virus or any other pathogen, your body reacts to it and produces antibodies. That is what you measure in a antibody response."
He says antibody test simply measures IGG antibody in a blood sample and it can be done using a fingerprick.
A patient who couldn’t get tested earlier or self-recovered can be identified with the help of an antibody test. This can give the government a clear estimation of how much of the population is actually infected or was infected.
'Not for Diagnostic'
Dr Shahid further explains why antibody tests are not for diagnostic purposes. He adds:
"Antibody tests can only be used for diagnosing people who already show symptoms. A negative antibody test doesn’t mean you don’t have it. PCR is a more conclusive test. An antibody test will also miss anything that happens early. So people who are in early phase of the disease, who don’t show symptoms or who’ve shown symptoms for only day or two will be missed by antibody tests."
He also specifies that antibody tests that are being proposed are going to be used more for population screening because there is also a need to know how many people are actually infected by this virus in a population.
He adds, "Unless you know that, you can’t really put good public health mitigation measures to control this infection".
What the Studies Say about Antibody & PCR Tests?
Dr Shahid also talks about two studies related to the appearance of antibodies and PCR. He says, "The results from these two studies say that PCR is positive in nasopharyngeal swabs from day 0 to day 14 and we are measuring it from the time of onset of symptoms because before symptoms you can’t tell who is infected and who is not so most of the testing is done on patients after the symptoms appear. Nasopharyngeal swabs are positive for PCR from day 0 to day 14, sputum is positive between day 0 to day 33 and stool is positive between day 0 and day 20. "
He further adds, "There are a few caveats to this. Firstly, there isn’t enough virus being passed out in stool, so although stool continuous to be a source of infection, the load of virus is much higher in nasopharyngeal swabs and sputum. This also means that once somebody becomes negative for PCR in nasopharyngeal swabs, they are still positive in sputum, which means sputum can continue to be a source of infection."
Talking about the antibodies' response to the virus, he says, "IGM response is a strong response that comes around day 7 post symptoms and lasts till around day 45 post symptoms. The IGG response appears around day 10 post symptoms and continues till about day 50 and that was the point at which they terminated measurements. The understanding is that IGG would continue much longer. So IGM does not continue, it’s a transient response, IGG is a more persistent response and lasts longer."
What ICMR Says in Its Initial Advisory?
In a new advisory released on Saturday, 4 April, ICMR said that if a person is tested positive for antibody test, after clinical assessment, they will be treated in hospital or put in isolation as per protocol. Action as per protocol to be initiated for contact tracing.
However, if a person tests negative, they will either be put in home-quarantine or if warranted they will be tested for PCR.
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