Hiii ... I've used blood (serum &plasma) for my phD proect to extract microRNA 

First .The storage should be in -80 is better ... even no problem with storge on microRNA expression

Second ... ive extracted microRNA  using norgen kit and gives good concentration and purity

Third... if you have pax tubes ... alot of papers preferred it and when instart my work it not been available in that time 

Finally... data base u should read alot about microRNA papers. ....

mirBase is for the sequence. .

Good luck 

Hi Noha I'm working on miRNA from serum samples. Did you want to extract miRNA from total blood? In this case the best way are the paxgene tubes for blood storage. Otherwise you can isolate serum, plasma or buffy coat before extracting miRNA.

I use a specific kit for miRNA extraction but depends what kind of analyses you wanna do later.

Let me know what do you need

Main precautions are noted each suppliers kit manual, you will go through on it.

Must maintain the temperature of samples under liquid nitrogen, arrange all materials (the one is supplied with kit) and other will be required to prevent any difficulty when you start the purification, and strictly follow instructions of kit's manual.

Yes, you should use pax tubes, but must be kept immediately in liquid nitrogen.

Also for analysis of data you should learn about operating the softwares.