Separating blood. Laboratory technician squeezing a bag of donor blood to separate its components. The blood has been spun inside a centrifuge to increase the separation of its cellular components (erythrocytes or red blood cells, red) from the liquid component (plasma). The white blood cells (leucocytes) are usually removed by filters before this stage. This labour-intensive manual process can be replaced by automated machine separation, either in the laboratory or during donation. A bag in the background is seen labelled with an O blood group letter, an indication of its compatibility with other blood. For centrifuged blood that is ready for pressure separation, see image M532/658.