Short communication
Streamlining SARS-CoV-2 confirmatory testing to reduce false positive results

https://doi.org/10.1016/j.jcv.2021.104762Get rights and content

Highlights

  • False positive SARS-CoV-2 results occur which can lead to harm.

  • Confirmatory testing is critical to reduce false positive results.

  • Confirmatory testing has a drawback of increased turnaround time.

  • A threshold to trigger confirmatory testing can reduce turnaround time and workload.

Abstract

Background

Confirmatory testing of SARS-CoV-2 results is essential to reduce false positives, but comes at a cost of significant extra workload for laboratories and increased turnaround time. A balance must be sought. We analysed our confirmatory testing pathway to produce a more refined approach in preparation for rising case numbers.

Methods

Over a 10-week low prevalence period we performed confirmatory testing on all newly positive results. Turnaround time was measured and results were analysed to identify a threshold that could be applied as a cut-off for future confirmatory testing and reduce overall workload for the laboratory.

Results

Between 22/06/20 and 31/08/20 confirmatory testing was performed on 108 newly positive samples, identifying 32 false positive results (30 %). Turnaround time doubled, increasing by an extra 17 h. There was a highly statistically significant difference between initial Relative Light Unit (RLU) of results that confirmed compared to those that did not, 1176 vs 721 (P < 0.00001). RLU = 1000 was identified as a suitable threshold for confirmatory testing in our laboratory: with RLU ≥ 1000, 55/56 (98 %) confirmed as positive, whereas with RLU < 1000 only 12/38 (32 %) confirmed.

Conclusions

False positive SARS-CoV-2 tests can be identified by confirmatory testing, yet this may significantly delay results. Establishing a threshold for confirmatory testing streamlines this process to focus only on samples where it is most required. We advise all laboratories to follow a similar process to identify thresholds that trigger confirmatory testing for their own assays, increasing accuracy while maintaining efficiency for when case numbers are high.

Keywords

SARS-CoV-2
COVID-19
Confirmatory testing
False positive
Laboratory diagnosis

Cited by (0)

1

Joint first authorship.

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