Good test hunting: FDA authorizations point to benchmarks for COVID-19 serology
How to size up COVID-19 tests, using FDA authorizations as guideposts
The critical role of COVID-19 antibody testing in reopening society -- combined with controversy around the regulatory flexibility these tests have received and reports that some are performing poorly -- have put all eyes on evaluation metrics. FDA’s new guidelines for serological test validation by other government agencies provide a first glimpse into how the agency is defining high performance, and some of the tests it has approved itself fall short.
With COVID-19 testing universally seen as a cornerstone for returning to normal life, the obvious question is which tests will be informative and reliable enough to guide personal and public health decisions.
Industry, government and the general public have therefore become keen to understand the sensitivity, specificity and predictive value of tests on the market, how a test’s clinical relevance varies across populations, and the hurdles facing COVID-19 tests in particular (see “The Quarantiner’s Guide to Evaluating COVID-19 Tests”).
Figure: The quarantiner’s guide to evaluating COVID-19 tests
Tests with binary results are typically evaluated based on sensitivity and specificity, which are characteristics intrinsic to the test. Objectively defining sensitivity and specificity requires having a reference standard -- a test universally recognized as the best available method for establishing the presence or absence of a condition. When no reference standard is available, sensitivity and specificity are defined as positive percent agreement (PPA) and negative