3 Week Old Blood is not good for transfusion

As per a study blood older than three weeks may get spoiled and not be effective. After three weeks, the blood cells become more firm and so becomes difficult for it to enter the smaller capillaries. The cell membrane varies and the cell membrane that stiffens is prone to weaken the flow of blood through the smallest capillaries. It has been known for long that the blood gets damaged as it ages. The chemicals that help blood to deliver oxygen overturn themselves after a transfusion.