How can I predict the percent qPCR signal due to contaminating DNA, for a given qPCR assay, and its matching NRT control?
Assuming 100% amplification efficiency, each step increase in Ct value represents a doubling in the amount of qPCR template. Therefore, evaluating the difference in Ct values between the qPCR assay, and its matching NRT control, leads to the following predictions:
| CtNRT - Ct+RT | Fraction of gene expression signal due to contaminating DNA | Percentage of gene expression signal due to contaminating DNA |
| 1 | (1/21) = 1/2 | 50% |
| 2 | (1/22) = 1/4 | 25% |
| 3 | (1/23) = 1/8 | 13% |
| 4 | (1/24) = 1/16 | 6% |
| 5 | (1/25) = 1/32 | 3% |