Usually you do qPCR to assess how much is a target gene being transcribed (mRNA) and for that you should extract Total RNA and then do reverse transcription before the qPCR itself.

https://www.enzolifesciences.com/science-center/technotes/2017/march/what-are-the-differences-between-pcr-rt-pcr-qpcr-and-rt-qpcr?/

Dear Abdul Rouf, Pls check the link below. Hopefully, you can clear your idea.

https://www.researchgate.net/post/What-is-difference-between-qPCR-and-RTPCR

Hello Abdul Rouf

RT-PCR, also known as Reverse Transcriptase PCR, typically measures RNA expression levels. In RT-PCR, complementary DNA (cDNA) is made by reverse transcribing of the RNA template with the enzyme reverse transcriptase.

This technique is used to qualitatively study gene expression and can be combined with real time PCR (qPCR) to quantify RNA levels. RT-PCR is used in research laboratories to study gene expression, for example in experiments to distinguish exons from introns, and can be used clinically to diagnose genetic diseases and monitor drug therapy.

Also, RT-PCR is commonly used in the diagnosis and quantification of RNA virus infections (e.g., human immunodeficiency virus, hepatitis C virus, corona virus) and the analysis of mRNA transcripts such as those produced by translocations commonly associated with non-Hodgkin's lymphomas, leukemias, and sarcomas.

Gene expression profiling is likely to have a major impact on molecular diagnostics and will depend on RNA analysis using RT-PCR and possibly high-density arrays.

So, it is not always extracting DNA directly from the cells and then preparing the samples for qPCR. Sometimes, we have to go for reverse transcription step to prepare cDNA and then do qPCR.

Hope this information helps!

Best Wishes.

Article Difference Between PCR and RT PCR