Filterability of red cells in iron deficiency

A method of measuring red-cell filterability is described in which washed, human red cells, substantially freed of white cells and platelets and suspended in isotonic phosphate-buffered saline at 20–220°, are delivered at a constant rate and concentration to a membrane with 3 μm diameter pores. Filterability is determined as a pressure increase on the upstream side of the membrane arising from the passage of cells through the pores. Application of the technique to iron-deficient red cells demonstrated that at a fixed concentration of cells they are more filterable than normal. Published reports which show them to be less filterable probably arise from the use of a fixed haematocrit rather than a fixed red-cell concentration to express the results.