[Growth of calcium oxalate crystals in vitro: a simple method for measurement of the inhibitory action of human urine (author's transl)].

A technically simple and reproducible method is described for the determination of the growth of crystals of calcium oxalate monohydrate in vitro. In a system made metastable with respect to calcium and oxalate ion concentrations, the time course of crystal growth was measured by the decrease of free calcium ions, following the addition of a fixed quantity of calcium oxalate seed crystals. Inhibition of crystal growth caused by the addition of various inhibitors or urine was determined, and the possibility of supersaturation of crystal-forming ions was excluded by using low concentrations. The known inhibitors, ethane 1-hydroxy-1,1-bisphosphonate, heparin and chondroitin sulphate C were tested, and ethane 1-hydroxy-1,1-bisphosphonate showed the strongest inhibition of crystal growth. The inhibitory action of human urine was treated by addition of urine (30 ml/l) from resting and strongly hydrated probands.