Methods for the study of calcium oxalate crystallisation and their application to urolithiasis research

Many methods have been used to study calcium oxalate crystallisation. Most can be characterised by changes in supersaturation during the experiment, which may increase, remain constant or decay. Their ability to quantify various aspects of crystallisation often reflects the extent to which nucleation, growth and aggregation can be measured independently, when two or three of these processes may be occurring simultaneously. The mixed suspension, mixed product removal technique reaches a steady state supersaturation, is a good model for intrarenal crystallisation and allows both growth and nucleation rates to be measured. Using 92% urine and comparing control urines with samples from recurrent stone formers no difference in growth rates was found but the controls had higher nucleation rates (p = 0.003) and lower supersaturations (p = 0.001). In parallel crystallisers running simultaneously, heparin or hyaluronic acid addition to 92% urine was studied. Both macromolecules increased growth rates, decreased nucleation rates and increased supersaturation (p < 0.05). The steady state supersaturation achieved in this system may be an important determinant of stone forming potential. The ability to reach a lower urinary supersaturation by increased nucleation may be a crucial protective factor distinguishing non stone formers from stone formers.