how to use delta-delta Ct method? - when no expression in healthy controls! (Jan/20/2011 )

for me it is not clear, how to use the delta-delta Ct method, if my healthy controls not expressing this special gene (e.g. tumor marker)? I normally use a 45 cycle real time protocol, and some markers are undetermined.

hope tho get any suggestions, how to solve the problem,
thx

You can insert maximal cycle number (45 in your case)as Ct value for non-expressing cells and proceed as usual.

thx for recommendation.

another question arose: can I built a mean value of the delta Ct´s of all healthy controls to generate the delta delta ct for all samples (healthy & cancer patients)? = delta Ct of one sample minus the mean of the delta Cts of the healthy controls?