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Covid-19 lateral flow tests
Calculator for interpreting test results
© 2021 BMJ Publishing Group Ltd.
Interactive
Pre-test probability
Likelihood of
having covid-19
%
Test sensitivity
The proportion of
patients with covid-19
who have a positive test
%
Test specificity
The proportion of
patients without covid-19
who have a negative test
%
If 100 000 people were tested with these values
True positive
False positive
False negative
True negative
Lateral
flow test
positive
Lateral
flow test
negative
100%
Probability
of having
covid-19
if test is
negative
Adjust these
values to update
graphic below
people who test
positive have covid-19
100 000
100 000
people who test negative
do not have covid-19
person who tests positive
does not have covid-19
100 000
people who test
negative have covid-19
100 000
Probability
of having
covid-19
if test is
positive
100%
have covid-19
100 000
100 000
do not have covid-19
This calculator demonstrates how interpreting a covid-19 lateral flow device (LFD) result varies according
to the pre-test probability, and the sensitivity and specificity of the LFD used. LFDs are best for identifying
people with active infection. We recommend choosing values for test performance and pre-test
probability that reflect somebody having covid-19 and being infectious (see article below).
Please enter a number
between 0 and 100
Please enter a number
between 0 and 100
Please enter a number
between 0 and 100