Quantitative or semi-quantitative PCR: reality versus myth.

A l t h o u g h PCR is beginning to come of age, it is still quite common to read in the literature such statements as "PCR is not really a quantitative method" or "PCR has been shown at best to be a semi-quantitative procedure." Why is that in 1992 many people are still reluctant to associate PCR and quantitation of nucleic acids? I believe this misconception is the unfortunate result of a constant questioning of the credibility of PCR as being incapable of quantitative analysis. Initially, PCR was not viewed as having great quantitative power, an opinion exemplified by the fact that the first two books on PCR technology had no mention of quantitation. ~ Indeed, it should come as no surprise that the factor that makes PCR so powerful, i.e., its ability to amplify small amounts of nucleic acids, exponentially (3.4) is also the factor that makes the technique so challenging as a quantitative method. Anything that is capable of interfering with the exponential amplification might ruin the intrinsic quantitative ability of PCR. (s) Therefore, the art of quantitative PCR is devoted to minimizing the amount of interference with the actual doubling of the target amplicon at each cycle and compensating for the inescapable, even if minimized, interference with the very doubling.