Investigations on macromolecular precipitation inhibitors of calcium oxalate.

Certain important aspects of the urine oxalate tolerance test (OTT) have been revised. The stirring system has been changed and the test has been adapted to the kinetics of calcium oxalate precipitation. True equilibrium conditions are now ensured during the measurements. Furthermore, the endogenous oxalate concentration is determined and taken into consideration. As a result of these changes, the significance of the test results has greatly improved. The effects of the addition of small amounts of zinc on the precipitation of calcium oxalate have been used in a new variation of the OTT. This new test makes it possible to discriminate much faster and more simply between recurrent stone-formers and other subjects. Tamm-Horsfall protein (THP) has been tested for its effect on the precipitation of calcium oxalate by means of OTT. THP inhibits the precipitation of calcium oxalate, but THP of stone-formers has a diminished inhibitory activity. The inhibitory activity of this protein strongly depends on the method by which it is isolated.