The Raw Cycle Threshold Values From Reverse-transcription Polymerase Chain Reaction Detection Are Not Viral Load Quantitation Units
Guillermo Aquino‐Jarquín
Abstract
To theEditor—I read with great interest the recent publication by Yu and colleagues [1] regarding quantitative detection and viral load analysis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in infected patients. The authors asserted that the results of reverse-transcription polymerase chain reaction (RT-PCR) and droplet-digital polymerase chain reaction (ddPCR) for SARS-CoV-2 detection were consistent in 95 positive samples and the cycle threshold (Ct) values of RT-PCR were highly correlated with the copy number values of ddPCR. However, the Ct values per se cannot be directly interpreted as viral load without a standard curve, which is the most direct and precise approach for analyzing quantitative data using a reference, such as in-house plasmid controls, with known viral copy numbers [2]. The linearity of the standard curve is denoted by the R2 value (Pearson correlation coefficient) and should be very close to 1. The...