Urine volume increases and urine specific gravity decreases in cats with nephrolithiasis or urolithiasis

Abstract

The etiology of urinary tract stones in cats is not clear. Among others, concentrated urine is considered a risk factor. The objective of this study was to compare urine measurements in stone‐forming cats with those in healthy cats.Four cats with kidney (3 cats) or urinary bladder (1 cat) stones and 11 healthy cats were used. Stone‐forming cats were 6 to15 years old (median = 12.7 years) and healthy cats were 5 to 13 years old (median = 10.8 years). The stone‐forming cats were confirmed with x‐ray radiography and/or ultrasonography.Cats were fed a commercial dry cat food for 4 weeks. Forty‐eight hour urine was collected during the last two days of the study. The urine was collected continuously in the collection receptacles kept at 38 °C.Comparing with healthy cats, stone‐forming cats had significantly increased urine volume (87 ml/day vs. 145 ml/day, p < 0.05) and decreased urine specific gravity (1.033 vs. 1.025, p < 0.05). Urine pH was similar between the groups (5.94 vs. 5.88, p = 0.604). Urinary NH4+, Na, K, P, and Oxalate were significantly lower in stone‐forming cats (p < 0.05). Urinary Cl, Ca, Mg, S, and Citrate were similar between the groups (p > 0.05). These data show that urine was not concentrated in cats with existing stones in the urinary tract. The mechanism underling the increased urine volume and decreased urine specific gravity in stone‐forming cats is unclear and needs further investigation.