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Clinicians' Probability Calculator to Convert Pre-Test to Post-Test Probability of SARS-CoV-2 Infection Based on
Zoe Brooks1, Saswati Das2, Tom Pliura3
1Awesome Numbers, Worthington, Ontario, Canada.
Background:
Despite best efforts, false positive and false negative test results for SARS-CoV-2 are unavoidable. Likelihood ratios convert a clinical opinion of pre-test probability to post-test probability, independently of prevalence of disease in the test population.
Methods:
The authors examined results of PPA (Positive Percent Agreement, sensitivity) and NPA (Negative Percent Agreement, specificity) from 73 laboratory experiments for molecular tests for SARS-CoV-2 as reported to the FIND database, and for two manufacturers' claims in FDA EUA submissions.PPA and NPA were converted to likelihood ratios to calculate post-test probability of disease based on clinical opinion of pre-test probability. Confidence intervals were based on the number of samples tested. An online calculator was created to help clinicians identify false-positive, or false-negative SARS-CoV-2 test results for COVID-19 disease.
Results:
Laboratory results from the same test methods did not mirror each other or the manufacturer. Laboratory studies showed PPA from 17% to 100% and NPA from 70.4% to 100%. The number of known samples varied 8 to 675 known patient samples, which greatly impacted confidence intervals.
Conclusion:
Post-test probability of the presence of disease (true-positive or false-negative tests) varies with clinical pre-test probability, likelihood ratios and confidence intervals.The Clinician's Probability Calculator creates reports to help clinicians estimate post-test probability of COVID-19 based on the testing laboratory's verified PPA and NPA.
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