Effect of sample vortex mixing on severe acute respiratory syndrome coronavirus 2 nucleic acid testing: Comparative analysis of individual samples and sample pools.

ObjectiveThis study investigated the effect of sample vortex mixing on the cycle threshold (Ct) values of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleic acid testing and further explored the underlying reasons for this effect.MethodsWe initially examined the impact of sample vortex mixing on Ct values. Subsequently, epithelial cells within the samples were quantified and stained using an improved Neubauer hemocytometer and Wright-Giemsa stain to elucidate the causative factors of Ct value changes. Finally, we expanded our sample size to validate the effect of vortex mixing on Ct values.ResultsWe observed a significant decrease in Ct values (all <0.001) and an increase in epithelial cell concentration (all <0.001) following vortex mixing compared with no vortex mixing. Specifically, the Ct values of individual samples decreased after 2 min of vortex mixing compared with 30 s of vortex mixing (<0.001). However, the Ct values of the sample pools increased after 2 min of vortex mixing (<0.05). Validation with an expanded sample yielded similar results.ConclusionsOur findings demonstrate that vortex mixing substantially decreases sample Ct values. These results contribute to the standardization of nucleic acid testing procedures.