Clinicians’ Probability Calculator to Convert Pre-Test to Post-Test Probability of SARS-CoV-2 Infection Based on Method Validation from Each Laboratory

Brooks, Zoe; Das, Saswati; Pliura, Tom

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.