CCQM-P199b: Interlaboratory comparability study of SARS-CoV-2 RNA copy number quantification
Authors: Devonshire Alison S. , Busby Eloise J. , Jones Gerwyn M. , O’Sullivan Denise M. , Fernandez-Gonzalez Ana , Hernandez-Hernandez Laura , Dai Xinhua , Dong Lianhua , Niu Chunyan , Xie Jie , Wang Xia , Qiao Xiaoting , Fang Xiang , Morris Clare , Almond Neil , Cleveland Megan H. , Vallone Peter M. , Castro Galván Esther , Pérez Urquiza Melina , Guadalupe Herrera López Mercedes , Khan Arifa S. , Fuentes Sandra M. , Emerson Leguizamon Guerrero John , Luis Davila Gonzalez Sergio , Felipe León Torres Andres , Folgueras-Flatschart Aurea V , Neves de Medeiros Marcelo , Marcos Saraiva Antonio , Becht Flatschart Roberto , Divieto Carla , Pegoraro Mattia , Zucco Massimo , Revel Laura , Mazzara Marco , Corbisier Philippe , Buttinger Gerhard , Yang Inchul , Bae Young-Kyung , Bogožalec Košir Alexandra , Milavec Mojca , Hawkins Malcolm , Sanzone A. Pia , Morris Phattarapornn , Temisak Sasithon , Lynch David , McLaughlin Jacob , Forbes-Smith Michael , Hall Felicity , Burke Daniel , Shibayama Sachie , Fujii Shin-ichiro , Kato Megumi , Falak Samreen , Macdonald Rainer , Kummrow Andreas , Komissarov Andrey , Komissarova Kseniya , Akyurek Sema , Akgoz Muslum , Nur Sanal Demirci Sumeyra , Vonsky Maxim , Runov Andrey , Kulyabina Elena , Rebrikov Denis , Huggett Jim F. 
Published: March 2024

Nucleic acid amplification tests including reverse transcription quantitative PCR (RT-qPCR) are used to detect RNA from Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the causative agent of the Coronavirus disease 2019 (COVID-19) pandemic. Standardized measurements of RNA can facilitate comparable performance of laboratory tests in the absence of existing reference measurement systems early on in a pandemic. Interlaboratory study CCQM P199b “SARS-CoV-2 RNA copy number quantification” was designed to test the fitness-for-purpose of developed candidate reference measurement procedures (RMPs) for SARS-CoV-2 genomic targets in purified RNA materials, and was conducted under the auspices of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM) to evaluate the measurement comparability of national metrology institutes (NMIs) and designated institutes (DIs), thereby supporting international standardization.

Twenty-one laboratories participated in CCQM P199b and were requested to report the RNA copy number concentration, expressed in number of copies per microliter, of the SARS-CoV-2 nucleocapsid (N) gene partial region (NC_045512.2: 28274-29239) and envelope (E) gene (NC_045512.2: 26245-26472) (optional measurements) in samples consisting ofin vitrotranscribed RNA or purified RNA from lentiviral constructs. Materials were provided in two categories: lower concentration (≈ (101-104) /μL in aqueous solution containing human RNA background) and high concentration (≈ 109/μL in aqueous solution without any other RNA background).

For the measurement ofNgene concentration in the lower concentration study materials, the majority of laboratories (n= 17) used one-step reverse transcription-digital PCR (RT-dPCR), with three laboratories applying two-step RT-dPCR and one laboratory RT-qPCR. Sixteen laboratories submitted results forEgene concentration. Reproducibility (% CV or equivalent) for RT-dPCR ranged from 19 % to 31 %. Measurements of the high concentration study material by orthogonal methods (isotope dilution-mass spectrometry and single molecule flow cytometry) and a gravimetrically linked lower concentration material were in a good agreement, suggesting a lack of overall bias in RT-dPCR measurements. However methodological factors such as primer and probe (assay) sequences, RT-dPCR reagents and dPCR partition volume were found to be potential sources of interlaboratory variation which need to be controlled when applying this technique.

This study demonstrates that the accuracy of RT-dPCR is fit-for-purpose as a RMP for viral RNA target quantification in purified RNA materials and highlights where metrological approaches such as the use ofin vitrotranscribed controls, orthogonal methods and measurement uncertainty evaluation can support standardization of molecular methods.