The PerkinElmer New Coronavirus Nucleic Acid Detection Kit authorized under FDA EUA incorporates multiple control steps to prevent the reporting of both false positive and false negative results.
Ct Cut-Off Values
The use of Ct cut-off values for reporting positive ensures the accuracy of your results. Ct cut-offs for interpretation are set close to the Limit of Detection (LOD) for the assay. The Ct (cycle threshold) is defined as the number of amplification cycles required for the fluorescent signal to cross the threshold (ie exceeds background level). SARS-CoV-2 real-time RT-PCR assays detect two or more targets in the coronavirus genome. If a target is detected but is above the Ct cut-off value, it is considered a weak positive. However, the presence of one gene target within the defined Ct range for SARS-CoV-2 is all that is needed to determine if a sample is positive. If one gene target is detected weakly and the other targets in the assay are not detected, the sample needs to be re-tested. If inconclusive results are obtained a second time, the sample needs to be re-tested either by re-extracting fresh RNA from the existing sample or by collecting a new sample from the patient and testing the new sample. For more information read our blog post, How to Handle Inconclusive Samples with SARS-CoV-2 Real-time PCR Tests.
Whole Process Controls
Additionally, the PerkinElmer New Coronavirus Nucleic Acid Detection Kit includes full process controls including, positive, negative, and exogenous internal controls. These aid in the interpretation of results by identifying contamination during processing, inhibition of the reverse transcription and amplification reactions, or even if the pre-PCR step of extraction was successful or not. Learn the importance of incorporating full process controls into your SARS-CoV-2 testing and how to interpret the results generated using these controls in the blog post, SARS-CoV-2 RT-PCR Controls.
Reduction of Cross Contamination During RNA Isolation
Cross contamination can also lead to false positives. The chemagen™ extraction system reduces the possibility of cross contamination by incorporating a bead transfer technology based on using magnetic rods to move RNA bound to magnetic beads through the binding, washing, and elution steps of RNA purification.
Most other nucleic acid isolation systems move liquids during the RNA isolation process. This bead transfer technology eliminates potential for contamination which can be caused by dripping tips or sample aerosolization.