Asymptomatic Patient Testing After 10:1 Pooling Using the Xpert Xpress SARS-CoV-2 Assay. Issue 4 (5th January 2021)

• Record Type: Journal Article
• Authors: Procop, Gary W; Tuohy, Marion; Ramsey, Christine; Rhoads, Daniel D; Rubin, Brian P; Figler, Richard
• Is Part Of: American journal of clinical pathology. Volume 155:Issue 4(2021)
• Page Start: 522
• Page End: 526
• Publication Date: 2021-01-05
• Subjects: SARS-CoV-2 -- COVID-19 -- Pooling -- Xpert Xpress SARS-CoV-2 assay -- Coronavirus; Diagnosis, Laboratory -- Periodicals; Pathology -- Periodicals; 616.07
• DOI: 10.1093/ajcp/aqaa273
• Languages: English
• ISSNs: 0002-9173

Abstract

Abstract: Objectives: Pool testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) preserves testing resources at the risk of missing specimens through specimen dilution. Methods: To determine whether SARS-CoV-2 specimens would be missed after 10:1 pooling, we identified 10 specimens with midrange (ie, 25-34 cycles) and 10 with late (ie, >34-45 cycles) crossing threshold (Ct) values and tested these both neat and after 10:1 pooling. Final test results and Ct changes were compared. Results: Overall, 17 of 20 specimens that contained SARS-CoV-2 were detected after 10:1 pooling with the Xpert Xpress SARS-CoV-2 Assay (Cepheid), rendering an 85% positive percentage of agreement. All 10 of 10 specimens with an undiluted Ct in the mid-Ct range were detected after 10:1 pooling, in contrast to 7 of 10 with an undiluted Ct in the late-Ct range. The overall Ct difference between the neat testing and the 10:1 pool was 2.9 cycles for the N2 gene target and 3 cycles for the E gene target. The N2 gene reaction was more sensitive than the E gene reaction, detecting 16 of 20 positive specimens after 10:1 pooling compared with 9 of 20 specimens. Conclusions: An 85% positive percentage of agreement was achieved, with only specimens with low viral loads being missed following 10:1 pooling. The average impact on both reverse transcription polymerase chain reactions within this assay was about 3 cycles.