WEAPONS IN THE WAR ON COVID-19

No treatment. No vaccine. Only physical distance, a limited stock of protective equipment and diagnostic tests. It’s not a very promising start. Hardly surprising, then that we’re falling back on the certainty provided by lab tests. Those who live out their working lives in pathology labs are in demand like never before.

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A good deal of the overtime the colleagues have been putting in has been spent explaining the limits we place around critical lab test performance to achieve consistent accuracy. It’s not simply a matter of picking up a “test kit” and running it out of your kitchen, office or garage. Pathology services rely on a complex process of validating tests, calibrating them against known standards and operating them under carefully audited conditions. Accreditation agencies perform inspections periodically to check that the test service is operating to a satisfactory standard, and recommend correction if needed.

This is why no pathology test method, no matter how urgent the demand, can be used without establishing test performance, purpose, scope of practice, controls, reporting processes, quality control, training and reagent supply. Even in the midst of an escalating pandemic, which threatens to overwhelm pathology services in developed countries, we do not have the resources to validate every diagnostic test pumped out by biotech companies. Priorities have to be set, and adhered to.

So, what’s this about a rapid diagnostic finger-prick test we heard so much about this week?  Unless the Micrognome has missed something, the only rapid feature of the tests being peddled by a predatory arm of the biotech industry is speed of completion.

Let’s unwrap this: finger prick blood tests for antibodies against SARS-CoV-2 have less than 100% sensitivity. Indeed, the limited published data suggest that the sensitivity of these assays is less than the specificity; the opposite to what you need in an early screening test. But an even more fundamental shortfall is that these tests rely on antibody forming to the SARS-CoV-2 virus during acute infection. The test will therefore only register recent (around 5 days) or previous infection (around 14 days): not early infection before it has become firmly established.

At present, internationally recognised infectious disease experts have used nucleic acid amplification (RT-PCR assays) as the most sensitive way to detect COVID-19 in returning international travelers. While we’re still unsure of how to detect pre-symptomatic infection, it is very unlikely to be by antibody detection.

The proposal to screen the entire UK population is based on universal access to PCR assays.

So, for the meantime, the main weapons at our disposal remain swabs, PCR assays, PPE and physical distancing.

COVID-19 reader.

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