A lesson from COVID-19 on the dangers of using Cq to quantify nucleic acids

SARS-CoV-2 RNA quantities, measured by reverse transcription quantitative PCR (RT-qPCR), have been proposed to classify individuals at greater likelihood of spreading infection as well as performance targets for IVD development and approval. A recent study investigated the reproducibility of quantification cycles (Cqs) – also referred to as cycle threshold (Ct) or crossing point (Cp) – and how setting diagnostic cutoffs altered the clinical sensitivity of COVID-19 testing.

During this panel discussion, our expert panelists will discuss why the study recommends that Cq values not be used in this way and will leverage their lessons learned from the pandemic to improve SARS-CoV-2 measurements and promote reproducibility across labs worldwide. Topics will include measurement science (metrology) and units, the potential impact on diagnostic performance and the development of IVDs, how the measurement science assisted external quality assessment providers and how this work was able to support thresholding in a real clinical setting. The panelists will also discuss the potential clinical impact of their findings as well as explore how the performance of diagnostic tests may be linked to the stage of the pandemic. For instance, is it better to deploy analytically less sensitive tests as a screening tool when the pandemic is growing rather than when it is more stable or decreasing?

Key Learning Objectives:

• Choice of unit is important when quantifying virus
• Cq values are not reliably reproducible
• The quantity of RNA or DNA matters even for qualitative tests
• The R value of a virus may impact the performance of less sensitive tests

Who Should Attend?

• Those who are interested in developing, deploying and responsible for guidance/regulation of IVD tests as well as more general researchers using qPCR as a tool to measure nucleic acids.