Hello Raghda A. Mohammed

There is a debate over whether serum or plasma is the most appropriate sample type to detect both miRNA and RNA expression. Several studies have found that plasma samples provide a higher recovery of miRNA (based on real-time RT-PCR), although others have seen no or minimal difference between serum and plasma.

I feel serum sample would be more appropriate because additional RNA may be released from cells during the coagulation process. Cell lysis, especially the highly abundant red blood cells, during the coagulation process is one of the possible explanations for the RNA concentration difference between serum and plasma. During the coagulation process, blood cells are exposed to a stressful environment which in turn may stimulate the release of certain miRNAs and RNAs. Additionally, the platelets also contain significant amounts of RNA which might also be released into the serum during the coagulation process.

I have attached a few articles below which you may want to refer.

https://assets.thermofisher.com/TFS-Assets/LSG/manuals/MAN0017497_miRNASerumPlasma_RG.pdf

Article Kroh EM, Parkin RK, Mitchell PS, Tewari MAnalysis of circula...

Article Analysis of Circulating MicroRNA: Preanalytical and Analytic...

Article Comparing the MicroRNA Spectrum between Serum and Plasma

Best.

blood samples are the most appropriate for RNA expression detection