Impact of Pool Testing in Detection of Asymptomatic Patients With COVID-19

David L. Smalley, PhD; Patricia M. Cisarik, OD, PhD; James Grantham; William Cloud, MD; R. Brock Neil, PhD; Paul DePriest, MD


Lab Med. 2021;52(1):e15-e16. 

In This Article

Materials and Methods

Upon approval from the Institutional Review Board of the Baptist Memorial Hospital system (Memphis, TN), the nasopharyngeal specimens of 9 patients who tested positive for SARS-CoV-2 using single-specimen RT-PCR and who had been clinically determined by a medical professional to be asymptomatic were retrieved from a bank of frozen specimens (–70ºC). Each nasopharyngeal swab collected had been placed in a viral transport medium and sent to the laboratory for testing. The specimens were initially tested with the Roche Cobas 8800 using the Roche SARS-CoV2-RT-PCDR kit (Roche Diagnostics, Indianapolis, IN). After the positive results manifested, the specimens had been frozen at –70ºC in a specimen bank. For the pooled testing, each specimen was thawed to room temperature and sequentially diluted to create 3:1, 5:1, and 7:1 aliquot specimens, which were then placed in a sterile viral transport medium. The 3:1 aliquot used a ratio of 400 μL of specimen to 800 μL of transport medium, the 5:1 aliquot used 200 μL of specimen to 800 μL of transport medium, and the 7:1 aliquot used 100 μL of specimen to 600 μL of viral transport medium. The aliquot specimens were tested immediately on the Roche Cobas 8800, and the retrospectively collected threshold cycle (Ct) values were evaluated. Because of the limited specimens available, specimens 6, 7, 8, and 9 were only tested at a 5:1 dilution.