Estimation of platelet size by measurement of intracellular water space using an oil technique

The intracellular water space of human platelets has been measured after equilibration with tritiated water and then separating these cells by centrifugation through phthalate oil of density 1.042. The mean intracellular water space of platelets in citrated plasma was 0.52 +/- 0.09 microliter/10(8) cells for 19 normal subjects. The gravimetric water content of platelets was 784 +/- 4 mg water/g cells. From these values the mean platelet volume was calculated to be 6.2 fl which agrees closely with values based on Coulter size distribution and thrombocytocrit. Gel filtration alters platelets such that a mean 19% of the platelets could not be centrifuged through phthalate oils of density 1.031 or 1.042. The measurement of tritiated water space of platelets centrifuged from their own plasma through oil provides a simple and reliable estimate of the mean platelet size.