Is it possible to extract RNA from RNAprotect-stabilized-blood?
The use of RNA later is NOT recommended for blood.
To recover samples already stored in RNAprotect, it is possible to try QIAzol at 10:1 ratio (QIAzol:blood) and follow the RNeasy Plus Universal kit protocol. Please note that the result is not guaranteed.
In case of RNAprotect, it is possible to spin down blood cells, remove the supernatant and continue with the cellular fraction only, so the processing volume will not become quite as large. However, that is only an option if the blood has not been frozen (before or after addition of RNAprotect), because RNA from cells that burst upon thawing would be lost.