THE DEPENDENCE OF THE MEASUREMENT OF CRYSTAL-GROWTH ON THE STATE OF CRYSTAL AGGREGATION - IMPLICATIONS FOR UROLITHIASIS RESEARCH

Two different methods for the analysis of data produced by a Coulter c ounter were used to obtain rates of calcium oxalate crystal growth and aggregation occurring in a seeded crystallization system: (1) crystal growth was expressed as the increase in crystal volume, and aggregati on as the decrease in crystal numbers observed by the Coulter counter; (2) crystal growth was expressed as the linear increase in crystal di ameter, calculated using a computer model which, when calculating exte nts of aggregation, takes account of any crystals moving into and out of the field of view of the instrument. Data from experiments using di fferent concentrations of seed crystals were analysed by these two met hods. Expressing crystal growth as the increase in volume showed growt h rates to be directly proportional to the total surface of seed cryst als present, while expressing the same growth as the linear increase i n crystal diameter showed growth rates to be independent of this varia ble. This difference in expression of experimental data became importa nt when urine was included in the experimental system, and varying deg rees of crystal aggregation affected the amount of surface area availa ble for crystal growth. Expressing growth as the increase in crystal v olume, and aggregation as the uncorrected decrease in crystal number, resulted in overestimation of inhibitory activities of urine towards c rystal growth and aggregation by 60% and 40%, respectively. Calculatio n of crystal growth rates from the linear increase in crystal diameter , and aggregation rates from data corrected for the crystals moving th rough the field of view of the particle counter, are essential for the valid interpretation of such data.