Removing PCR duplicates in RNA-seq Analysis After reading some of the forum posts in Biostar and SeqAnswers I find it very confusing whether to filter out the duplicate reads from aligned files or not. As far I understand it's very difficult to distinguish between highly expressed genes and duplicate reads and we may lose important information during the filtration process.

So, is it really necessary to remove the duplicates in differential expression analysis using RNA-seq data?
For normal RNA-seq PCR duplicates are normally kept in, but the duplication rate can be used as a quality control: The higher the duplication rate, the lower the quality. For expression analysis, it is probably best to discard high duplication rate samples, rather than deduplicate them. 

In general, the smaller the amount of RNA input into the library prepartion the worst the duplication. Many protocols for very low input quantities (such as single cell) include random barcodes called UMIs (Unique Molecular Identifiers). These allow PCR duplicates to be distinguished from genuinely independent molecules that just happen to have the sample mapping position.