Does it make sense to put your money on a diagnostic test that does not give you an accurate result on whether you have the coronavirus infection? Well, that’s the question being asked in scientific circles, of serological or antibody tests that are much sought after these days by governments across the world.

The rapid antibody test can tell you if the body is producing antibodies as an immune response to an ongoing Covid infection or to an earlier bout of the illness. But there’s a hitch, as antibodies are produced by the body several days (about 14 or more) into the infection.

So tests done on individuals during the in-between asymptomatic period would pick up no antibody readings. And these people would have been sent home on that negative reading. But the trouble begins if, days later, these people show Covid symptoms, having in the meanwhile infected many others they may have interacted with.

Experts across the world are pointing to these loopholes in rapid antibody tests that let patients fly below the radar. The Rajasthan government has become the first in India to point to the low efficacy of these tests.

Countries should be investing in strengthening their diagnostic backbone with more sturdy and accurate tests (like the RT-PCR — reverse transcription polymerase chain reaction) and address shortages in reagents used in testing etc, rather than chase rapid tests that serve at best in mapping a trend, with some leeway being made for the inaccurate readings.

In fact, there are other shortcomings too. For instance, a person recovering from the Covid infection would have antibodies in their blood, but it’s unclear if this would protect him or her from getting reinfected. The World Health Organization’s precise words on this: “There is no evidence to date to support this.”

Red flags are increasingly being raised on the low quality of some of these hastily put-together rapid antibody tests (with reported accuracy of 30 per cent) and calls are getting louder for greater sophistication and validation of these tests.

The UK recently burnt its fingers buying 3.5 million rapid tests from China, only to find them unfit for use, as reports suggest. The WHO’s experts have pointed to the drawbacks of serological tests and caution against making them the centre-piece of plans to lift lockdowns and return to work. And the US Food and Drug Administration too cautions that “serological tests should not be used as the sole basis to diagnose or exclude infection with the SARS-CoV-2 virus,” as testing an asymptomatic person would throw up wrong results.

On its part, the Indian Council of Medical Research has played safe in listing out 14-odd validated kit-makers. The ICMR says upfront these tests are not recommended for the detection of the infection. It cryptically adds: “Positive test indicates exposure to SARS-CoV-2; Negative test does not rule out Covid-19 infection”.

That being the case, should governments be relying so heavily on these tests?

In its favour, data experts say that even flawed readings of Covid-positive cases give planners some indication of trends in a population. But that too, only if the testing has been done systematically in a cluster, weeks apart and in the right manner.

According to the USFDA, antibody tests can help in identifying people with antibodies so they can donate blood to help manufacture convalescent plasma, an investigational product used in those seriously ill from Covid-19.

But preliminary diagnosis is a life-and-death situation and the scientific community is clear in its ask. Define and strengthen the network for preliminary diagnosis and treatment, and do not blur this space with tests that are beneficial in mapping trends.

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