The present status of blood filtration.

The history of the development of blood transfusion and blood filtration is outlined. Clinical and experimental evidence for the efficacy of microfiltration in both small and large volume transfusions is evaluated. Though microfilters do remove the micro-aggregates from stored blood, the results of clinical studies suggest that both the debris from septic processes in the body and the formation of micro-aggregates in the blood stream triggered by processes such as complement activation play a far more important role in the pathogenesis of adult respiratory distress syndrome. If this is so the enhancement of the reticulo-endothelial system by fibronectin therapy may be indicated. It also follows that the use of microfilters is probably an unnecessary expense and, where exsanguination is a risk, may be positively dangerous. Microfilters have been found useful in the preparation of granulocyte-free transfusions after centrifugation of the blood, but their routine use for transfusions, small or large, remains to be justified.