Packed RBCs consist of refrigerated stored blood with about three fourths of the plasma removed. Packed cells help avoid the problem of overloading the patient’s blood volume and instigating pulmonary edema. This is especially useful in patients with anemias due to destruction or poor production of RBCs, when the plasma volume does not need replacement. In fact, when anemia is due to pure RBC deficiency, plasma volume becomes greater than usual, because extracellular fluid tends to replace the missing RBC volume to maintain total blood volume. Packed cells are sometimes used when the donor RBCs type satisfactorily but antibodies are present in donor plasma. Packed cell administration also helps diminish some of the other problems of stored blood, such as elevated plasma potassium or ammonium levels. Packed RBCs retain about 20%-25% of the plasma and most of the white blood cells (WBCs) and platelets. Preserved in CPDA-1, on day 1 plasma potassium averages about 5.1 mEq/L (mmolL) and on day 35 averages about 78.5 mEq/L (mmolL), due in part to the small amount of plasma remaining with the RBC. Plasma Hb on day 1 averages about 78 mg/L and on day 35 averages about 658 mg/L (also partially due to small plasma volume).