Guidelines posted for tests to screen asymptomatic people for COVID-19
The U.S. Food and Drug Administration (FDA) has posted a template on its website outlining the validation process that developers of molecular diagnostic tests should follow if they intend their assays to be used for pooling patient samples or for screening asymptomatic individuals not suspected of having COVID-19, the agency said in a news release.
“The FDA recognizes that organizations may want to conduct screening of asymptomatic individuals as part of a broader strategy to help ensure the safety of their employees, patients, students and others. In addition to these template updates, the FDA has made available FAQs with information regarding tests for screening asymptomatic individuals,” said Jeffrey E. Shuren, MD, JD, Director of the Center for Devices and Radiological Health at the FDA.
The template addresses a testing technique known as “pooling” samples. In this technique, labs mix several samples together in a “batch” or pooled sample and then test the pooled sample with a diagnostic test, the FDA said.
If the pooled sample is negative, labs can deduce that all patients in the batch were negative. If the pooled sample comes back positive, labs then test each sample individually to find out which ones are positive. By using the pooling technique, labs can run fewer tests overall, meaning fewer testing supplies are used, and results can be returned to patients more quickly.
However, because samples are diluted, which could result in less viral genetic material available to detect, there is a greater likelihood of false negative results, particularly if not properly validated. The FDA said the pooling method works well when there is a low prevalence of cases, meaning more negative results are expected, as would likely be the case when testing a large volume of asymptomatic people.
