Maybe I am missing something in your question,  but generally cDNA is reverse  transcribed RNA.    cDNAs are made by isolating RNA (either total or poly-A+) and using either poly-dT or random primers to reverse transcribe it. 

Hi Anil

I agree with Gregory, Anil. cDNA and reverse transcribed RNA are the same thing so I'm not sure what you're asking or trying to do. Are you trying to isolate specific cDNA and trying to distinguish that  from the total cDNA pool?

Regards,

Nathaniel

Hi 

cDNA is received after RT on RNA. And this is important because you can't work with RNA directly  if you want to do PCR, sequencing etc

Explain us what is your experiment, and what is the purpose.

have a good luck