Rapid failures: On antibody testing kits

Significant error rates for COVID-19 antibody testing kits underscore the need for caution

Updated - April 24, 2020 12:27 am IST

Published - April 24, 2020 12:15 am IST

Rapid testing kits that State governments have been using to detect antibodies to the novel coronavirus have proved unreliable, making the shift to normal life after the lockdown ends on May 3 more difficult. Governments around the world have been looking for an accurate blood test that can tell people if they have immunity through past COVID-19 infection, and can therefore return to their duties to kickstart the economy. While the diagnostic RT-PCR test to confirm the presence of the virus using a nasal swab in a laboratory setting is considered reliable, attempts to design a rapid test that uses a blood sample to find antibodies after past infection have thrown up errors in as much as a third of cases: a study in the U.K. showed that they were high on specificity — accurate in cases that they found to be antibody positive. But they still missed about 30% of positive cases, showing low sensitivity. This is the phenomenon worrying India, which has imported several hundred thousand rapid testing kits, and its experience is shared by the U.S., U.K., Spain and other countries. Rajasthan had laboratory-confirmed COVID-19 positive cases not being detected by rapid testing kits . Several States have independently ordered thousands of kits, mainly from China, and are in a quandary.

The ICMR has advised States , to whom it distributed kits, that they could be used for surveillance testing, rather than to make medically important decisions. Narrowing down the test to reliable methods is the challenge, and the WHO along with its collaborating centres is working to identify them. The results will be crucial and all countries, including the U.S. White House Coronavirus Task Force, are looking at serosurveillance, the process that will determine the status of the population on COVID-19. An exit from lockdown and other public health measures depend on such testing. India should remain focused on identifying tests that work well. This requires close integration with efforts launched by diagnostics regulators in the U.S., Europe and China who have used emergency provisions to allow early use of kits; the kits themselves are under evaluation. There are reports indicating that some vendors of rapid testing devices in China have run afoul of regulators in that country since they have no prior expertise in the field. Making purchase decisions, therefore, calls for rigorous review. In the immediate context, the message should go out to States that rapid tests cannot substitute for RT-PCR to diagnose infection. It is by no means clear that antibodies developed in response to COVID-19 provide long-term protection against reinfection. Yet, a good test to certify a large section of the population as having developed immunity seems to be a promising tool to reopen the economy with some confidence.

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