Retention of platelets by glass bead filters.

Whole blood was passed through glass bead filters and the retention of platelets studied under various experimental conditions. Platelet retention was similar over a wide range of blood flow rates; however, it was decreased at fast rates of flow. Platelet retention was not influenced by the haematocrit value of the blood over a wide range. Retention in filters containing siliconized beads was similar to that in filters with untreated beads. Platelet retention was inhibited by the addition of citrate or adenosine to the blood before passage through the filter and was also less when the blood was cooled. Heparin and phenylindandione therapy did not affect the results. There was a wide range of results of platelet retention tests with normal blood samples and considerable variability between the results of duplicate samples from the same donor. Repeated testing of normal donors over a three-month period gave results which varied widely within the normal range. Twenty-two of 40 uraemic blood samples showed decreased platelet retention. The mechanism of platelet retention from whole blood by glass bead filters is not clear but may be related to platelet aggregation induced by adenosine diphosphate or other aggregating agents.