Nationwide harmonization effort for semi-quantitative reporting of SARS-CoV-2 PCR test results in Belgium

Lize Cuypers, Jannes Bode, Kurt Beuselinck, Lies Laenen, Klaas Dewaele, Reile Janssen, Arnaud Capron, Yves Lafort, Henry Paridaens, Bertrand Bearzatto, Mathieu Cauchie, Aline Huwart, Jonathan Degosserie, Olivier Fagnart, Yarah Overmeire, Arlette Rouffiange, Ilse Vandecandelaere, Marine Deffontaine, Thomas Pilate, Nicolas YinIsabel Micalessi, Sandrine Roisin, Veronique Moons, Marijke Reynders, Sophia Steyaert, Coralie Henin, Elena Lazarova, Dagmar Obbels, François E Dufrasne, Hendri Pirenne, Raf Schepers, Anaëlle Collin, Bruno Verhasselt, Laurent Gillet, Stijn Jonckheere, Philippe Van Lint, Bea Van den Poel, Yolien Van der Beken, Violeta Stojkovic, Maria-Grazia Garrino, Hannah Segers, Kevin Vos, Maaike Godefroid, Valerie Pede, Friedel Nollet, Vincent Claes, Inge Verschraegen, Pierre Bogaerts, Marjan Van Gysel, Judith Leurs, Veroniek Saegeman, Oriane Soetens, Merijn Vanhee, Gilberte Schiettekatte, Evelyne Huyghe, Steven Martens, Ann Lemmens, Heleen Nailis, Kim Laffineur, Deborah Steensels, Elke Vanlaere, Jérémie Gras, Gatien Roussel, Koenraad Gijbels, Michael Boudewijns, Catherine Sion, Wim Achtergael, Wim Maurissen, Luc Iliano, Marianne Chantrenne, Geert Vanheule, Reinoud Flies, Nicolas Hougardy, Mario Berth, Vanessa Verbeke, Robin Morent, Anne Vankeerberghen, Sébastien Bontems, Kaat Kehoe, Anneleen Schallier, Giang Ho, Kristof Bafort, Marijke Raymaekers, Yolande Pypen, Amelie Heinrichs, Wim Schuermans, Dominique Cuigniez, Salah Eddine Lali, Stefanie Drieghe, Dieter Ory, Marie Le Mercier, Kristel Van Laethem, Inge Thoelen, Sarah Vandamme, Iqbal Mansoor, Carl Vael, Maxime De Sloovere, Katrien Declerck, Elisabeth Dequeker, Stefanie Desmet, Piet Maes, Katrien Lagrou, Emmanuel André

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From early 2020, a high demand for SARS-CoV-2 tests was driven by several testing indications, including asymptomatic cases, resulting in the massive roll-out of PCR assays to combat the pandemic. Considering the dynamic of viral shedding during the course of infection, the demand to report cycle threshold (Ct) values rapidly emerged. As Ct values can be affected by a number of factors, we considered that harmonization of semi-quantitative PCR results across laboratories would avoid potential divergent interpretations, particularly in the absence of clinical or serological information. A proposal to harmonize reporting of test results was drafted by the National Reference Centre (NRC) UZ/KU Leuven, distinguishing four categories of positivity based on RNA copies/mL. Pre-quantified control material was shipped to 124 laboratories with instructions to setup a standard curve to define thresholds per assay. For each assay, the mean Ct value and corresponding standard deviation was calculated per target gene, for the three concentrations (107, 105 and 103 copies/mL) that determine the classification. The results of 17 assays are summarized. This harmonization effort allowed to ensure that all Belgian laboratories would report positive PCR results in the same semi-quantitative manner to clinicians and to the national database which feeds contact tracing interventions.

Original languageEnglish
Article number1294
Issue number6
Number of pages17
Publication statusPublished - 2022


  • Belgium/epidemiology
  • COVID-19/diagnosis
  • Humans
  • Pandemics
  • Real-Time Polymerase Chain Reaction
  • SARS-CoV-2/genetics


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