may 2020 • BMJ

Interpreting a covid-19 test result

Watson J., Whiting P. F., Brush J. E.

DOI: 10.1136/bmj.m1808

Content curation::Nuno Parente

Key message

A interpretação do resultado de um teste para o covid-19 depende de duas coisas: a precisão do teste e a probabilidade pré-teste ou risco estimado de doença antes do teste; Um teste de RT-PCR positivo para o teste covid-19 tem mais peso do que um teste negativo devido à alta especificidade do teste, mas com sensibilidade moderada; Um único teste covid-19 negativo negativo não deve ser usado como regra em pacientes com sintomas fortemente sugestivos; Os médicos devem compartilhar informações com os pacientes sobre a precisão dos testes covid-19.


Across the world there is a clamour for covid-19 testing, with Tedros Adhanom Ghebreyesus, director general of the World Health Organization, encouraging countries to “test, test, test.” The availability of the complete genome of covid-19 early in the epidemic facilitated development of tests to detect viral RNA. Multiple assays with different gene targets have been developed using reverse transcriptase polymerase chain reaction (RT-PCR). These viral RNA tests use samples usually obtained from the respiratory tract by nasopharyngeal swab, to detect current infections. Serology blood tests to detect antibodies indicating past infection are being developed; these will not be considered in depth in this article. /n /n Testing for covid-19 enables infected individuals to be identified and isolated to reduce spread, allows contact tracing for exposed individuals, and provides knowledge of regional and national rates of infection to inform public health interventions. However, questions remain on how to apply test results to make optimal decisions about individual patients.