The U.S. Food and Drug Administration (FDA) has taken steps to encourage the development of tests for screening asymptomatic individuals and for testing pooled samples, as summarized in the June 16, 2020, FDA Statement Facilitating Diagnostic Test Availability for Asymptomatic Testing and Sample Pooling. The FDA has continued to work with developers to facilitate testing of pooled samples, including providing more detailed recommendations in the July 6, 2020, and July 28, 2020, updates to the EUA templates.
The FDA encourages developers to consider validating their tests for the screening of asymptomatic individuals and for testing pooled samples.
The FDA has provided these resources about testing using pooled samples and testing for asymptomatic screening:
- Emergency Use Authorization (EUA) Templates: Include validation recommendations for tests, including for screening of asymptomatic individuals and pooled sample testing.
- FAQs on Testing for SARS-CoV-2: Includes Frequently Asked Questions, including about screening of asymptomatic individuals and pooled sample testing, and discusses the differences between surveillance, screening, and diagnostic testing.
The FDA is aware that there is a great interest in performing testing using pooled samples. Pooling samples involves mixing several samples together in a "batch" or pooled sample, then testing the pooled sample with a diagnostic test. This approach increases the number of individuals that can be tested using the same amount of resources. For example, four samples may be tested together, using only the resources needed for a single test. 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. This method of pooling samples works well when there is a low prevalence of cases, meaning more negative results are expected than positive results.
The FDA believes that sample pooling can be authorized for use in certain SARS-CoV-2 tests with appropriate mitigations and validation. The FDA has provided validation recommendations for tests intended for use with pooled samples in the EUA Templates.
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Test developers seeking authorization for their test for use with pooled samples should validate their test for such use, considering the validation recommendations outlined in the EUA templates, and submit an EUA request to the FDA.
Generally, the FDA recommends validating the test with either pooling approach in a way that preserves the sensitivity of the test as much as possible. That is, it is preferable to use an approach where all specimens identified as positive when tested individually are also identified as positive when tested using the pooled testing approach. However, a decrease in performance is likely with pooling strategies, due to dilution of the primary clinical sample.
As discussed in the templates, since sample pooling will greatly increase the number of individuals that can be tested using existing resources, a small reduction in sensitivity may be acceptable depending on the pooling efficiency and other mitigations in place.
Therefore, the FDA generally recommends that, after pooling, test performance includes ≥85% percent positive agreement (PPA) when compared with the same test performed on individual samples. Additional limitations, such as considering negative results from pooled samples to be presumptive negatives, may be recommended based on the patient population included in the sponsor's clinical evaluation and the performance data submitted in the EUA request.
As discussed in the templates, a plan for ongoing monitoring of the positivity rate and of the performance of a test with a pooling strategy should be included in the test's procedures. As data become available and new approaches are identified, our recommendations in these templates may evolve.
Complete sample testing and screening information is available on the FDA website.