Diagnostics


Put to the test A


squinting eye and an urge to gag have been two unpleasant experiences shared by many during the pandemic, as the testing process for Covid-19 PCR test requires a vigorous swabbing of the tonsils, followed by lodging the same swab so far up your nose it feels like the brain itself is getting a prodding.


Most people accept that it’s necessary, of course – a little short-term discomfort endured to prevent yourself from becoming a spreader. In some countries, like the UK, there’s likely to be a lateral flow test prior to the confirmatory PCR, but it’s the latter that is


Practical Patient Care / www.practical-patient-care.com


considered highly accurate by virologists. Although the breadth of studies on PCR suggest its exact sensitivity is hard to pin down, a recent study entitled ‘Screening for SARS-CoV-2 by RT-PCR: Saliva or nasopharyngeal swab? Rapid review and meta-analysis’ looked at 48 studies and found an overall sensitivity of 92% for nasopharyngeal samples and 86% for saliva samples. But despite the advantage of high sensitivity, which translates into a low rate of false negatives, PCR tests could never power the mass testing strategies many governments have used to try and control the spread of Covid-19.


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When it comes to accurate Covid-19 testing, PCR is the acronym on most people’s lips. It’s for a good reason – after all, the test earned the accolade of “gold standard” diagnostic by having the highest sensitivity and specificity in the marketplace. But the laboratories that process these tests weren’t prepared for the sort of volume the pandemic brought, and the reality for many has been at least a two-day wait to find out whether they’re Covid free. Peter Littlejohns looks at how diagnostic technology has developed in response to the pandemic and speaks to some of the innovators behind it to understand how we can be better prepared to control another wave.


Harvard Wyss Institute


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