CALCIUM-OXALATE NEPHROLITHIASIS, A FREE OR FIXED PARTICLE DISEASE

The chances of stone formation occurring through a free particle mecha nism were calculated using the approach of Finlayson and Reid [1]. For these calculations we used new data on nephron dimensions, supersatur ation and crystal growth rates in urine, and also incorporated the siz e increasing effect of crystal agglomeration. The calculations were pe rformed assuming different levels of oxalate excretion, simulating the diurnal variation and acute hyperoxaluria following a dietary load. I n addition urinary flow conditions were varied according to changes in daily urinary volume. It is shown that during the normal transit time of urine through the nephron, particles can obtain a size big enough to be retained in the nephron. This is mainly due to the size-increasi ng effect of the agglomeration process. The precipitable amount of oxa late present is not limiting for the maximum attainable particle size. However, acute increases in oxalate excretion do pose a risk because supersaturation is reached earlier in the nephron and consequently the crystal particles are allowed more time to increase in size. In concl usion, the present calculations demonstrate that during the normal tra nsit time through the kidney, crystalline particles can be formed whic h are large enough to be retained because of their size and thus form the nidus of a stone. The highest risk is encountered at the end of th ose collecting ducts where crystals formed in nephrons with a long loo p of Henle meet and agglomerate.