Packed Red Blood Cells
450 ml of donated blood turns into about 250. This happens in a centrifuge. Prior to being centrifuged, citrate is added to plasma; this results in a chelation of calcium. In the absence of free calcium ions, the coagulation cascade grinds to a halt. The cells are thus separated from their plasma, and put into a bag. In addition to cells, various preservatives are added, and they maintain red cell viability during their long cold storage. In storage red cells also modify their own environment by constantly spewing the products of anaerobic metabolism into it. Furthermore, some red cells lyse, and their corpses further pollute the contents of the bag. The milieu inside a unit of packed red cells becomes quite noxious, and over the years some concerns have been raised that transfusions of "aged" cells (i.e. ones which have been stored over a longer time) have increased the mortality of trauma patients and the elderly.
Cellular content of Packed Red Blood Cells
The Australian Red Cross Blood Service claim that their house red contains 40g of hemoglobin per 200ml bag, which would come to a Hb of 200 per litre, at a hematocrit of 0.5 to 0.7. This resembles the full blood count of a polycythaemic person from the foothills of the Himalayas.
Electrolyte content of Packed Red Blood Cells
Surprisingly, nobody seems to have ever picked up a bag of packed cells and done an EUC and CMP on it. I would love to know the results. Whats the osmolality? How much citrate remains in there? Who knows. There are some articles where electrolytes in red cells are measured, and there is the transfusion.com.au website where red cell additive solutions are described (though not the reasons for their addition!)
Different companies seem to offer different mixtures of additives. In the figures above, I used the Fresenius constituents.