False negative rate of COVID-19 PCR testing: a discordant testing analysis

Virol J. 2021 Jan 9;18(1):13. doi: 10.1186/s12985-021-01489-0.


Background: COVID-19 is diagnosed via detection of SARS-CoV-2 RNA using real time reverse-transcriptase polymerase chain reaction (rtRT-PCR). Performance of many SARS-CoV-2 rtRT-PCR assays is not entirely known due to the lack of a gold standard. We sought to evaluate the false negative rate (FNR) and sensitivity of our laboratory-developed SARS-CoV-2 rtRT-PCR targeting the envelope (E) and RNA-dependent RNA-polymerase (RdRp) genes.

Methods: SARS-CoV-2 rtRT-PCR results at the Public Health Laboratory (Alberta, Canada) from January 21 to April 18, 2020 were reviewed to identify patients with an initial negative rtRT-PCR followed by a positive result on repeat testing within 14 days (defined as discordant results). Negative samples from these discordant specimens were re-tested using three alternate rtRT-PCR assays (targeting the E gene and N1/N2 regions of the nucleocapsid genes) to assess for false negative (FN) results.

Results: During the time period specified, 95,919 patients (100,001 samples) were tested for SARS-CoV-2. Of these, 49 patients were found to have discordant results including 49 positive and 52 negative swabs. Repeat testing of 52 negative swabs found five FNs (from five separate patients). Assuming 100% specificity of the diagnostic assay, the FNR and sensitivity in this group of patients with discordant testing was 9.3% (95% CI 1.5-17.0%) and 90.7% (95% CI 82.6-98.9%) respectively.

Conclusions: Studies to understand the FNR of routinely used assays are important to confirm adequate clinical performance. In this study, most FN results were due to low amounts of SARS-CoV-2 virus concentrations in patients with multiple specimens collected during different stages of infection. Post-test clinical evaluation of each patient is advised to ensure that rtRT-PCR results are not the only factor in excluding COVID-19.

Keywords: COVID-19; Discordant testing; False negative rate; SARS-CoV-2.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • COVID-19 / diagnosis*
  • COVID-19 / virology
  • COVID-19 Nucleic Acid Testing* / statistics & numerical data
  • Canada
  • False Negative Reactions
  • Female
  • Humans
  • Male
  • Middle Aged
  • Molecular Diagnostic Techniques / statistics & numerical data
  • Real-Time Polymerase Chain Reaction*
  • SARS-CoV-2 / isolation & purification*
  • Sensitivity and Specificity