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Interpreting Test Results

Interpreting test results

Giving you a clear view

Reliable results are important to help you to confidently create treatment plans that fit your patients’ needs. The BD Veritor™ Plus System provides rapid, reliable results to provide you the information you need to determine appropriate treatment plans for your patients quickly and efficiently.

Key topics related to diagnostic testing are explained below; you will find more information in our resource library.

Interpreting diagnostic test results

Timely and reliable results from rapid antigen testing allow caregivers to more quickly determine appropriate treatment plans. The BD Veritor™ Plus System provides rapid, reliable results that are easy to interpret – which can help give peace of mind to you and your patients in 15 minutes or less1-6.

Understanding clinical performance

You’ve performed the test, now it’s time to understand the results. While unusual, false positive results are a possible outcome in any diagnostic test. In the case of antigen tests, results could be influenced by workflow inconsistencies, quality of the sample itself, or protocol failure, to name a few.

When testing for SARS-CoV-2 in particular, It is important to understand how local disease prevalence rate and test performance characteristics may interact to influence the proportion of false positive test results compared to all positive results. The infographic below demonstrates how very low, low, medium and high prevalence rates make a difference. It is important to note that your institution’s specific prevalence rates can be used to calculate the potential for false positives in your facility. Understanding that false positive test results are a possibility is important. Please follow your institution and/or state and local guidance for addressing a patient with a positive test result. Guidance may include precautionary isolation procedures and a second mode of testing for confirmation.

Resource: https://www.cdc.gov/csels/dsepd/ss1978/lesson3/section2.html

 

SARS-CoV-2 hypothetical false positive rates based on prevalence¹

This image describes hypothetical false positive rates based on prevalence. Assuming a specificity rate of 99.5% and a sensitivity rate of 84%, testing a population with a very low prevalence (0.06%) of SARS-CoV-2 (2,000 tests) could yield a positive predictive value of 9.1%. In this hypothetical scenario, there would be 1 true positive and approximately 10 false positives.
This image describes hypothetical false positive rates based on prevalence. Assuming a specificity rate of 99.5% and a sensitivity rate of 84%, testing a population with a moderate prevalence (6%) of SARS-CoV-2 (2,000 tests) could yield a positive predictive value of 92%. In this hypothetical scenario, there would be 100 true positives and approximately 10 false positives.
This image describes hypothetical false positive rates based on prevalence. Assuming a specificity rate of 99.5% and a sensitivity rate of 84%, testing a population with a low prevalence (0.6%) of SARS-CoV-2 (2,000 tests) could yield a positive predictive value of 50%. In this hypothetical scenario, there would be 10 true positives and approximately 10 false positives.
This image describes hypothetical false positive rates based on prevalence.  Assuming a specificity rate of 99.5% and a sensitivity rate of 84%, testing a population with a high prevalence (12%) of SARS-CoV-2 (2,000 tests) could yield a positive predictive value of 96%. In this hypothetical scenario, there would be 200 true positives and approximately 10 false positives.

 

Note: we are using a figure of 99.5% specificity in these calculations. The PPV values reflect this calculation and are within the stated confidence intervals stated in the Instructions for Use.

Learn more about clinical questions related to COVID-19, including false positives

False positives based on prevalence

The BD Veritor™ System for Rapid Detection of SARS-CoV-2 has a 98%-100% specificity, which means the false positive rate 2% or less of all the tests performed1. This means, you might see 0-2 false positives for every 100 tests you conduct.  Any false positive should be reported to BD for further investigation. 

BD Veritor™  Plus System makes it easy to perform accurate tests. Find educational resources here.

For CDC information on prevalence rates:

CDC offers guidance for rapid antigen testing:

REFERENCES

  1. BD Veritor System for Rapid Detection of SARS-CoV-2 [package insert]. 256082. Franklin Lakes, NJ: Becton, Dickinson and Company.