Modern blood filters do not need to be routinely changed for the majority of red blood cell transfusions in New Zealand.

Two experimental studies were undertaken to determine if blood flow rate changes and/or red blood cell damage occurs during red cell transfusion via a single blood filter In the first study, 12 experiments were performed in each of which four units of group specific human red blood cells, followed by 500 ml 0.9% saline were sequentially run through a blood filter/intravenous giving set system connected to a 14 gauge intravenous cannula positioned two metres below the filter The second study involved ten experiments with ten units per experiment using the same methodology. In each study, flow rates of each red cell unit/saline were measured. Average flow rates did not decrease with subsequent red cell units in either the four- or ten-unit studies. There was no significant change in blood flow rates across the ten-unit transfusion (P = 0.4). In both studies, blood was taken before and after the blood filter from the first, fourth and tenth units of red blood cells, and was measured for haemoglobin, haematocrit, lactate dehydrogenase, potassium, haemolysis levels and red cell morphology. Haemolysis and lactate dehydrogenase levels decreased after blood filtration. Red cell morphology was unchanged in the four-unit study and tended to improve in the ten-unit study. We found no evidence that red blood cell damage is increased during such transfusion.