Concentration of a potent calcium oxalate monohydrate crystal growth inhibitor in the urine of normal persons and kidney stone patients by ELISA-based assay system employing monoclonal antibodies.

Standardized calcium oxalate monohydrate (COM) crystal growth assay system was employed to study the ability of various test samples to influence growth rates of COM crystals. The inhibitory activity (IA) of various samples was expressed in terms of inhibitory units. Urine samples obtained from normal persons and kidney stone patients were found to have IA of 3.18 +/- 0.62 and 1.02 +/- 0.08, respectively. A potent inhibitor having molecular weight between 14.2 and 16.2 kDa was found to be primarily responsible for the differences observed in the urinary IAs between normal persons and kidney stone patients. The potent inhibitor was found to be tightly associated with a chromophore resembling Urobilirubin. An ELISA based assay system, using monoclonal antibodies against the above most potent inhibitor confirmed the difference observed in the urinary IA between the normal persons and kidney stone patients. This assay system has the potential to be routinely used to screen human beings for potential stone formers.