EFFECT OF STIR BAR SIZE AND SHAPE ON QUANTITATIVE PLATELET-AGGREGATION

The effect of stir bar size and shape on quantitative platelet (human) aggregation induced by ristocetin, soluble collagen, a connective tissue suspension, ADP and epinephrine was studied under controlled conditions. In general, stir bars which mixed more effectively (as determined by a dye dilution assay) gave greater aggregation. Small differences in stir bar length resulted in significant differences in aggregation and could make the difference between the presence or absence of 2nd waves of ADP and epinephrine aggregation. The 2nd wave of epinephrine aggregation was enhanced by stir bars cut from steel wire, apparently as a result of forces generated by the sharp edges. Quantitative platelet aggregation should be carefully controlled for stir bar size and shape in addition to mixing speed.