Discrepancy between PCR based SARS-CoV-2 tests suggests the need to re-evaluate diagnostic assays

Muhammad Zain Mushtaq, Sadia Shakoor, Akbar Kanji, Najma Shaheen, Asghar Nasir, Zeeshan Ansar, Imran Ahmed, Syed Faisal Mahmood, Rumina Hasan, Zahra Hasan

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


Objective: We investigated the discrepancy between clinical and PCR-based diagnosis of COVID-19. We compared results of ten patients with mild to severe COVID-19. Respiratory samples from all cases were tested on the Roche SARS-CoV-2 (Cobas) assay, Filmarray RP2.1 (bioMereiux) and TaqPath™ COVID19 (Thermofisher) PCR assays. Results: Laboratory records of ten patients with mild to severe COVID-19 were examined. Initially, respiratory samples from the patients were tested as negative on the SARS-CoV-2 Roche® assay. Further investigation using the BIOFIRE® Filmarray RP2.1 assay identified SARS-CoV-2 as the pathogen in all ten cases. To investigate possible discrepancies between PCR assays, additional testing was conducted using the TaqPath™ COVID19 PCR. Eight of ten samples were positive for SARS-CoV-2 on the TaqPath assay. Further, Spike gene target failures (SGTF) were identified in three of these eight cases. Discrepancy between the three PCR assays could be due to variation in PCR efficiencies of the amplification reactions or, variation at primer binding sites. Strains with SGTF indicate the presence of new SARS-CoV-2 variant strains. Regular modification of gene targets in diagnostic assays may be necessary to maintain robustness and accuracy of SARS-CoV-2 diagnostic assays to avoid reduced case detection, under-surveillance, and missed opportunities for control.

Original languageEnglish
Article number316
JournalBMC Research Notes
Issue number1
Publication statusPublished - Dec 2021


  • COVID-19
  • PCR
  • SARS-CoV-2
  • Spike gene


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