Very interesting post. It is always interesting to see how techniques we take for granted in research labs is so well used and pipelined in clinical settings.

I usually wash fibroblast and epithelial cells from different tissues esp from skin on regular basis, before preparing them for culture or other experiments. The closest I have come to blood is isolating plasma from the mouse blood for testing the presence of Auto antibodies (anti-nuclear antibodies to be specific). I guessed that process of washing and isolating RBC involved some sort of rounds of centrifugation with some isotonic buffer. I wanted to know the buffering system here used to maintain the pH. I can see that saline is used to wash the RBCs. But what is the buffer? For e.g. I use Phosphate Buffer Saline (PBS) for diluting the plasma (pH=7.4). Here the saline bottle says pH = 5.5 (the pH of skin). I am little confused on why such low pH and what buffering system is used here?

Also, I was specifically looking for how do you isolate RBCs from other cellular components here. Is it some sort of gradient centrifugation that is used. Or is setting rcf/rpm sufficient to remove cellular impurities before the transfusion?