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Asymptomatic Patient Testing After 10:1 Pooling Using the Xpert Xpress SARS-CoV-2 Assay
Gary W Procop1, Marion Tuohy1, Christine Ramsey1
1Pathology and Laboratory Medicine Institute.
American Journal of Clinical Pathology
|January 5, 2021
Summary
Pool testing for SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) achieved 85% agreement, missing only low viral load specimens. This method impacts PCR assays by approximately 3 cycles, preserving testing resources.
Area of Science:
- Virology
- Molecular Diagnostics
- Public Health
Background:
- Pool testing for SARS-CoV-2 conserves resources but risks missing diluted specimens.
- Understanding the impact of dilution on SARS-CoV-2 detection is crucial for test accuracy.
Purpose of the Study:
- To evaluate the detection rate of SARS-CoV-2 specimens after 10:1 pooling.
- To determine the effect of pooling on crossing threshold (Ct) values using the Xpert Xpress SARS-CoV-2 Assay.
Main Methods:
- Ten SARS-CoV-2 specimens with midrange Ct values (25-34) and ten with late Ct values (>34-45) were tested neat and after 10:1 pooling.
- Results and Ct value changes were compared between neat and pooled testing.
Main Results:
- An 85% positive percentage of agreement was observed for 10:1 pooled SARS-CoV-2 testing.
- All 10 midrange Ct specimens were detected, while 7 of 10 late Ct specimens were detected after pooling.
- The N2 gene target showed higher sensitivity (16/20) than the E gene target (9/20) after pooling.
Conclusions:
- 10:1 pool testing for SARS-CoV-2 is effective, with missed detections primarily occurring in specimens with low viral loads.
- The average impact of 10:1 pooling on the assay's RT-PCR was approximately 3 Ct cycles.
- Pool testing offers a viable strategy for resource preservation in SARS-CoV-2 diagnostics.
