Calibrator undetectable - (Sep/29/2008 )

We are using the delta delta Ct calculation and would like T0 to be the calibrator. Some genes are undectable at this time point though, what do most people do in this situation? We have been thinking of setting the Ct value to 40.

Sometimes if you assign undetectable gene as 40 ct, it will give you troubles. For example, T0 gene 1 undetectable , and you treat it as ct=40, and compared to an internal control of Ct 29, and delta ct will be 11. In contrast, at T1 gene 1 ct is 29, and internal control ct 18, also delta ct will be 11. I would like to treat it as non-expressed for further analysis.