Separation of erythrocytes into age-related fractions by density or size? Counterflow centrifugation

During the process of aging red blood cells become denser and smaller. Counterflow centrifugation separates particles of lower density and smaller diameter from those of higher density and bigger diameter. Thus, the question arises: which property of the red cells, density or size, governs the age-related separation by counterflow centrifugation? It is shown that it is the size which dominates the balance between sedimentation and streaming. Age-related separation of human red blood cells by counterflow centrifugation (elutriation) was analysed by the standard hematological parameters (hemoglobin, mean corpuscular volume, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration), hemoglobin A1c and the membrane protein ratio 4.1a/(4.1a+4.1b). Red blood cells with a high hemoglobin A1c content and a high 4.1a/(4.1a+4.1b) ratio were found in the early fractions of the elutriation. This proves that old cells make up early fractions, while the "youngsters" constitute later ones. The elutriation technique used (yielding human red blood cells in a "healthy state") and the age parameters studied show that the membrane protein ratio 4.1a/(4.1a+4.1b) is another reliable age parameter for the assessment of red blood cell age.