In a randomized trial of canines with Staphylococcus aureus pneumonia (n=6 per group) which were transfused with either 7- or 42-day old washed or unwashed red blood cells (RBCs), researchers observed a significant improvement in survival when the 42-day old RBCs were washed.
In contrast, they found that washing 7-day old blood decreased canine survival. In addition, when 42-day old RBCs were washed, they found a lower concentration of non-transferrin bound iron, plasma labile iron, and cell-free hemoglobin and improved cardiac performance, shock index, and liver functions. Washing older blood may lyse fragile cells and remove excess iron thus improving the overall clinical outcome in a canine model of pneumonia, whereas washing fresher blood actually worsened the clinical outcome. There are currently five ongoing randomized trials in humans assessing the transfusion of older verses newer units of RBCs in humans.
1. Cortes-Puch I, Wang D, Sun J, Solomon SB, Remy KE, Fernandez M, Feng J, Kanias T, Bellavia L, Sinchar D, Perlegas A, Solomon MA, Kelley WE, Popovsky MA, Gladwin MT, Kim-Shapiro DB, Klein HG, Natanson C. Washing older blood units before transfusion reduces plasma iron and improves outcomes in experimental canine pneumonia. Blood 2014;123: 1403-11.