Effect of potassium citrate on calcium oxalate relative supersaturation (RSS)

Calcium oxalate (CaOx) uroliths are one of the most common types of stones in dogs with one recent study showing CaOx uroliths to be close to 50% of analyzed samples at one institution (Hunprasit 2019).

Relative supersaturation, or RSS, is a tool to assess the potential of urine to form crystals including those of calcium oxalate.  The lower the RSS that a diet induces, the lower the potential for a diet to contribute to stone formation (although many non-dietary factors can also have effects).

Potassium citrate is often considered as an adjunctive treatment to humans and pets with this type of urolith. Giving citrate salts potentially reduces urine calcium excretion and increases urinary citrate. Urine citrate also binds calcium in a soluble citrate complex which can reduce calcium salt supersaturations.

This study was designed to assess whether the addition of potassium citrate to a diet would significantly reduce RSS of CaOx. Three diets were evaluated.  All diets had a urinary therapeutic diet as a base with all acidifiers removed. The control diet did not have added potassium citrate, and the two test diets had added potassium citrate at levels of 1.5% (3.77 g/Mcal) and 3.0% (7.59 g/Mcal).

The diets were tested on two separate panels of dogs. One panel was dogs with predisposition for calcium oxalate stones (Miniature Schnauzers), while the other was not (Poodles). The standard Royal Canin protocol for RSS testing was used.  This included utilizing eight animals with a seven-day adaptation period and three days of urine collections which were pooled. Animal parameters such as body weight and food and water intake, as well as urine volumes were measured.  Urine specific gravity, urine pH, and the urinary concentrations of magnesium, calcium, sodium, potassium, phosphate, sulfate, ammonium, oxalate, citrate, uric acid, and creatinine were measured and entered into the Supersat software to calculate RSS. Linear mixed models were used to assess the influence of diet, panel and their respective interaction on the different parameters. The level of significance was set at 5%. 

For both panels it was found that the addition of potassium citrate decreased the CaOx RSS (as shown in the following tables and figure).  There was a significant effect of adding 1.5% potassium citrate, but no further effect with 3.0% potassium citrate.

The graphs below show the significant differences between the control diet and the 1.5% and 3.0% diets, but no significant differences between the 1.5% and 3.0% diets.

In conclusion, this study supports the use of potassium citrate to lower CaOx RSS. The addition of this substance to a diet formula might then help managing calcium oxalate urolithiasis.