Predicting the Crystallization Potential of Urine from Cats and Dogs with Respect to Calcium Oxalate and Magnesium Ammonium Phosphate (Struvite)

Abstract

The objective of this study was to validate two programs (SUPERSAT and EQUIL 2) for calculation of calcium oxalate (CaOx) and magnesium ammonium phosphate (struvite; MAP) relative supersaturation (RSS) in dog and cat urine. Healthy adult cats (n = 10) and dogs (n = 9) were fed standard diets for a 3-wk period. Urine was collected (24 h, dogs; 48 h, cats) and filtered, and the pH was measured. A 20-mL aliquot was titrated to pH 2 and frozen for analysis. Additional aliquots were incubated with 1 g seed crystals at 38°C; CaOx for 24 h (cat) and 2, 6 and 9 d (dog); MAP for 48 h (dog) and 6 d (cat). Samples were analyzed for 10 substances. RSS was calculated using EQUIL 2 and SUPERSAT. CaOx RSS (SUPERSAT): dog urine was initially supersaturated, whereas cat urine was undersaturated with the diets used. Cat urine reached the solubility product (K_sp), (RSS = 1) after 24-h incubation, whereas dog urine was still approaching K_sp at 9 d. MAP RSS (SUPERSAT): urine from both species was undersaturated and increased toward K_sp during incubation. Final RSS values were compared for both programs. SUPERSAT resulted in values close to 1 for both CaOx and MAP; EQUIL 2 gave similar values for CaOx RSS, although MAP RSS values were considerably higher than 1. In conclusion, EQUIL 2 and SUPERSAT both calculated reasonably accurate RSS values for CaOx, whereas only SUPERSAT provided an accurate measure of MAP RSS.