Many hospitals in India have started using CT to screen all emergency patients or patients due for admission for COVID-19. Is this valid, given that organizations like ACR and STR have advised against CT screening? We review a meta-analysis published recently in Radiology comparing CT with RT-PCR to explain how CT screening doesn’t help in India as of now.
Essentially, CT has high sensitivity but low specificity. Thus, the positive predictive value (PPV) of CT depends on the prevalence of COVID-19 in that particular region. In countries with <10% prevalence (where we assume India to still fall), the positive predictive value of RT-PCR (range: 47.3%, 84.3%) is more than ten times higher than that of CT scans, which is single-digit (range: 1.5%, 8.3%). Clearly not good enough to be used for screening!
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