[Model of calcium oxalate lithogenesis by kinetic turbidimetry]

The crystallization process of calcium oxalates in synthetic urine at 37 degrees C is followed by turbidimetry. As the solution absorbance is very sensitive to the number of particles in suspension, it is possible to distinguish nucleation and growth from agglomeration. In the former case, the slopes of the turbidimetric curves are positive whereas in the latter case, they are negative. Poisoning the solutions by some active additives induces changes of the slopes so that it becomes possible to know whether the additive is a promotor or an inhibitor of nucleation, growth or agglomeration. As an example, the model is tested for checking the influence of human urine on the crystallization process. It is shown that urine fractions of non stone-formers inhibit agglomeration when they contain macromolecules of high molecular weight (> 30,000 Da).