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Letters Covid 19: roll out of antibody testing

Rapid roll out of SARS-CoV-2 antibody testing—a concern

BMJ 2020; 369 doi: (Published 24 June 2020) Cite this as: BMJ 2020;369:m2420

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Re: Rapid roll out of SARS-CoV-2 antibody testing—a concern

Dear Editor

In line with expressed misgivings, and, picking out, at random, a source of antibody test kits, it is concerning to note in the manufacturer’s, ‘Limitations’ information, that the tests, have, “not been FDA cleared or approved…. Negative results do not rule out SARS-CoV-2 infection, particularly in those who have been in contact with the virus. Follow-up testing with a molecular diagnostic should be considered to rule out infection in these individuals….. Results from antibody testing should not be used as the sole basis to diagnose or exclude SARS-CoV-2 infection or to inform infection status …. Positive results may be due to past or present infection with non-SARS-CoV-2 coronavirus strains, such as coronavirus HKU1, NL63, OC43” (1).

It must therefore be asked, in view of the potential for cross-reactivity, why is the traditional use of ‘paired serology’ seemingly not being utilised in these cases? (2). And what consideration has been given to the phenomenon of, ‘Antibody Dependent Enhancement’? (3)

The RT-PCR test also appears to have its problems. Its inventor, Kary Mullis, who received the Nobel Prize for inventing the PCR manufacturing technique, is reported to have said that it was for research purposes only and not for medical diagnosis. An 80% false positive rate was reported from China in March 2020 (4).

A manufacturer of the, ‘SARS-CoV-2 RNA, Qualitative Real-Time RT-PCR (Test Code 39433)’ states in the package insert, “The agent detected may not be the definite cause of disease”. ‘Limitations’ include: “Negative results do not preclude SARS-CoV-2 infection and should not be used as the sole basis for treatment or other patient management decisions”.(5)

Indeed, a Swiss Institute of Microbiology reported that, antigen testing “methods based on real-time RT-PCR were recognised as reference protocols since mid-January, at the onset of the pandemic in China, and relayed – although not validated – by the World Health Organization”. They also found, ‘an incorrect degenerate base (S), that does not match with the SARS-CoV-2 RNA sequence’, and stated that other improvements to the RT-PCR test should be made in order to improve specificity.(6)

It is concerning that, at least in some cases, and maybe in all cases, neither antibody nor RT-PCR tests appear to be clinically validated nor sufficiently robust indicators on which to base recommendations for medical management or potentially major changes to individuals’ lives.


Competing interests: No competing interests

26 June 2020
Janet Menage
GP retired
Wales, UK