Total RNA extraction from whole blood

Hello.
I have to extract total RNA from whole blood using a guanidium-based
reagent, RNAiso plus (Takara).
Takara says that RNAiso plus is compatible with Trizol.
With 1mL of RNAiso plus, RNA from 100ul of whole blood can be processed.
In the Takara protocol, expected amount of RNA from 100ul human whole
blood is about 1.5~2ug.
However, in my case, the yield was quite low(about 150ng) and 28S and
18S rRNA bands disappeared after DNase I treatment.
I am stuck in this problem for 1 month.
Today I am extracting RNA again with two times of RNAiso plus treatment
If this does not work, I have no idea what to do next.
Does anybody have an experience with RNA extraction from whole blood
using RNAiso plus or Tri Reagent?

Thank you.

Sincerely,
Seong Hwan

--
Seong Hwan Park, M.D., Ph.D.
Instructor in Legal Medicine,
College of Medicine, Korea University
126-1 Anadong 5ga, Seongbukgu, Seoul 136-704
South Korea

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