AAT Bioquest

What is the significance of the cycle threshold?

Posted May 12, 2023


The Ct (cycle threshold) value represents the actual number of cycles required for a PCR test to detect the target nucleic acid sequence. It provides an estimate of the initial amount of the target sequence in the sample, rather than the exact amount. A low Ct value of less than 30 indicates that the target sequence is easier to detect in the sample, which means it is present in larger quantities in the sample. 

The Ct value is inversely proportional to the quantity of the target nucleic acid in the sample. Higher Ct values indicate lower viral loads and vice versa. This allows researchers to compare relative levels of the pathogen present in different samples.

Additional resources

The importance of cycle threshold values in interpreting molecular tests for SARS-CoV-2

Polymerase Chain Reaction (PCR)

ROX Reference Dye *50X fluorescence reference solution for PCR reactions*