The COVID-19 pandemic provides an excellent example of the trust we have in rapid screening tests.

The quality of a rapid test is judged by its sensitivity and specificity.

The sensitivity indicates the test’s ability to identify a positive case correctly, and the specificity is the test’s ability to identify a negative case correctly. These figures are obtained in a laboratory under ideal circumstances.

For COVID-19 rapid tests, manufacturers report a sensitivity and specificity of between 60% – 99%, which is an overestimation of the real-life sensitivity and specificity.

A sensitivity of 60% implies that 40% of the actual positive cases may be missed or that 4 out of 10 positive cases will be “False Negatives (FN)”. Similarly, if the specificity is 90%, 1 out of 10 patients will have a false-positive test result (FP). In a risk-sensitive environment, such as the current COVID-19 pandemic, one can reason that high sensitivity, less FN’s, is a requirement since the threat posed to the lives of the public is high.

The other side of the proverbial coin is that a FP result impacts individuals and their lively hoods. Therefore, it follows that these rapid test results require confirmation testing with PCR – South Africa does not have the resources to confirm every case. The urgency of decisive action forces us to isolate and wait until we cannot infect others anymore.

The same logic applies to drug screening tests with sensitivity and specificity of between 60% – 90%. The FP and FN rates are well documented and shockingly high for some real-life testing. An organisation cannot risk allowing an employee with a non-negative test result on-site. The result needs to be confirmed in the shortest possible time to reduce the impact on both parties while the
individual is temporarily removed from risk-sensitive duties.