Understanding false positives and the detection of SARS-CoV-2 using the Cepheid Xpert Xpress SARS-CoV-2 and BD MAX SARS-CoV-2 assays

Diagn Microbiol Infect Dis. 2021 May;100(1):115334. doi: 10.1016/j.diagmicrobio.2021.115334. Epub 2021 Feb 2.

Abstract

Several real-time RT-PCR assays have received Emergency Use Authorization from the United States Food and Drug Administration. The BD MAX™ SARS-CoV-2 assay, run by the BD MAX™ system, is a qualitative test that detects the SARS-CoV-2 specific nucleocapsid phosphoprotein gene regions, N1 and N2. The human RNase P gene is used as the endogenous nucleic acid extraction control. The Cepheid Xpert® Xpress SARS-CoV-2 assay, run by the GeneXpert system, detects the pan-sarbecovirus E gene and the N2 region of the N gene. We evaluated the performance characteristics of the BD and Cepheid assays using matched patient samples. We also analyzed comparative Ct values for both assays using 183 positive samples tested at this facility. In addition, we mitigated reporting false positive results without relying on interpretive software. We found that both systems showed comparable sensitivity. We found an approximately 3.5% false positive rate from the BD MAX™ system results.

Keywords: BD Max; False Positive; Real-time PCR.

Publication types

  • Comparative Study
  • Evaluation Study

MeSH terms

  • COVID-19 Nucleic Acid Testing / methods*
  • Coronavirus Envelope Proteins / genetics
  • Coronavirus Nucleocapsid Proteins / genetics
  • False Positive Reactions
  • Humans
  • Phosphoproteins / genetics
  • Real-Time Polymerase Chain Reaction / methods*

Substances

  • Coronavirus Envelope Proteins
  • Coronavirus Nucleocapsid Proteins
  • Phosphoproteins
  • envelope protein, SARS-CoV-2
  • nucleocapsid phosphoprotein, SARS-CoV-2