shRNA interference using Lenti virus vector - (Apr/07/2013 )

I wonder if anybody can help me figuring something out.
Iam going to perform a knockdown experiment for miRNA-21 in cell culture using shRNA lentivirus vector that express anti-miRNA molecule. This miRNA target irg1 gene. The question is: How can I be certain that my blocking of miRNA-21 cause changes in the level of irg1 gene ? as far as I know that q-PCR before and after the experiment for irg1 is not accurate ?

Have anybody an idea or advice

Why is the qPCR not accurate, it should be fine, and is usually the definitive measure when you are looking at KD of a RNA. You could do western blots to check the protein is also knocked down.