Calcium Oxalate Urolithiasis in Miniature Schnauzers

In the literature

Carr SV, Grant DC, DeMonaco SM, Shepherd M. Measurement of preprandial and postprandial urine calcium to creatinine ratios in male Miniature Schnauzers with and without urolithiasis. J Vet Intern Med. 2020;34(2):754-760.

The Research …

Calcium oxalate urolithiasis continues to be a focus of preventive care research in veterinary urology. Monitoring for stone occurrence and recurrence can be achieved through radiography and ultrasonography, but resolution and operator/technology limitations may prevent efficient monitoring. Current prevention options rely on dietary modification, alteration of pH, and decreasing calcium availability in the urine. This study used the urine calcium:creatinine (UCa:Cr) ratio to determine whether increased postprandial calcium excretion is associated with stone formation in male miniature schnauzers.

Dogs enrolled in the study were split into groups consisting of affected or previously affected stone formers versus breed-matched controls. All dogs were fed the same diet; urine samples were collected before the dogs ate in the morning, then at 1, 2, 4, and 8 hours after eating. Nine affected dogs were included in the study, 5 of which had both nephroliths and uroliths. When all collection time points were evaluated, dogs with elevated urine calcium levels (UCa:Cr >0.05) were 13 times more likely to form stones. The calcium level of the urine in these dogs was likely to be higher at the 1- and 8-hour sample collection times; however, multiple dogs with uroliths had elevated calcium throughout the day. In addition, the authors found a potential link between dyslipidemia and stone formation that may parallel human stone etiopathogenesis.¹

At UCa:Cr ratio levels >0.06, there was good specificity (93%) but poor sensitivity (56%) for predicting calcium oxalate urolithiasis, with a modest positive predictive value of 83%. Despite multiple postprandial timepoints, the UCa:Cr ratio was unable to detect an increase in postprandial calciuresis, which may be due in part to experimental design.

The ability to detect increased calcium in the urine is promising if this can be connected to stone formation. Future studies may focus more on trending urine calcium levels and stone formation.

… The Takeaways

Key pearls to put into practice:

• Owners of miniature schnauzers should be educated on the inherent risk for stone formation in their dog and how to identify urinary sand and grit prior to stone formation.

• If stones are passed, voided, or removed, they should be submitted for stone analysis, and management options should be discussed with the owner when results are available.

• Clinicians should stay apprised of the development of UCa:Cr ratio testing availability and consider this as a potential future tool for stone prevention.