The occurence and significance of microaggregates in stored blood.

During storage whole blood progressively forms microaggregates by adhesion of platelets and leucocytes. This occurs from the second day of storage and the presence of such potential microemboli can be demonstrated by light microscopy of smears of blood samples. They cause an increase in the viscosity of the blood as measurable by the screen filtration pressure method. If infused into a patient they, by causing microvascular occlusion, result in multiple organ dysfunction, primarily of the lung. It is recommended that, if whole blood greater than 4 days in storage is to be infused, an in-line microfilter be used to remove the microaggregates from the transfusion. Alternatively, early separation, or the use of fresh blood is recommended.