Optical Clearing Effect of Dextran on Human Platelet Suspensions

THE optical density of platelet-rich citrated plasma or of platelet suspensions has been seen to decrease irreversibly on the addition of a solution of dextran1. This decrease is biphasic, consisting of an immediate optical clearing effect independent of the molecular weight of the dextran fraction but related to its final concentration, and a delayed effect affected by molecular weight2. Because certain dextran fractions induce aggregation of human platelets1, it was at first assumed that the decrease in optical density of platelet-rich citrated plasma was caused by aggregation1. Only the delayed changes in optical density, however, seemed to correspond to the degree of platelet aggregation evaluated microscopically after the addition of dextran2. The immediate optical clearing effect of dextran has been further examined with a turbidimetric method and re-interpreted in the light of additional work on the optical properties of dextran.