The page below is a sample from the LabCE course Real-Time PCR. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Real-Time PCR Computer Results

The image on the right illustrates a result from a real-time PCR reaction. The y-axis is the level of fluorescence and the x-axis is the PCR cycle number. In this reaction there is a control reaction with a baseline of 30 fluorescence units (shown as a solid blue line) and the patient sample. By looking at the graph you can see that the sample exceeds the baseline fluorescence point at 18.93 cycles. This is the cycle threshold (Ct). The lower the Ct value the higher the original concentration of DNA, which requires fewer PCR cycles to build enough amplicons to cross the pre-established threshold.