This study evaluated and identified trends over time for the various types of minerals contained in feline uroliths analyzed by the Gerald V. Ling Urinary Stone Analysis Laboratory at the University of California-Davis, from 1985 through 2004. The calculi were removed from both the upper and lower portions of the urinary tract, with no distinction made between urethral plugs and urethral calculi. Results indicated that apatite uroliths decreased and dried solidified blood stones (DSBs) increased when compared with all other stone types. No trend for urate stones was noted. Females were more likely to have struvite and DSBs, whereas male cats were more likely to have calcium oxalate and brushite-containing stones. The ratio of calcium oxalate stones analyzed, as compared with struvite stones, increased significantly over the 20-year period. Struvite-containing stones had been the predominant mineral type found until 1993. The increasing proportion of calcium oxalate uroliths corroborated findings from other studies and could be a result of dietary modifications implemented to decrease urine pH to prevent recurrence of struvite formation. To then prevent recurrence of calcium oxalate uroliths, diets were formulated to produce a less acidic urine pH. When the 3 most recent years of the data set (2002 to 2004) are evaluated as 1 set, stone formation trends back toward struvite stone formation (44%) over calcium oxalate stone formation (40%). According to these observations, changes in mineral composition in uroliths in cats have occurred, and research studies designed to identify potential causes (diet, medical management, surgical technique) for these changes are required.

COMMENTARY: We have observed similar changes in composition of uroliths from cats. Between 1981 and 2006, the Minnesota Urolith Center analyzed more than 83,000 feline uroliths. Data indicate that the rise in calcium oxalate began in 1987 and reached peak levels in 1994 that persisted until 2001, at which time the levels began to subside. Although the present study did not distinguish urethral plugs from uroliths, our data indicate that the mineral composition of urethral plugs has not mirrored the changes observed in uroliths. Data from the Minnesota Urolith Center indicate that struvite has remained the most common mineral (83% of 5804 plug submissions) for more than 2 decades. Additional information may be obtained at our Web site: (click on the link to Department and Centers to find Minnesota Urolith Center). -- Jody Lulich, DVM, PhD, and Carl Osborne, DVM, PhD, Diplomate ACVIM

Evaluation of trends in urolith composition in cats: 5,230 cases (1985-2004). Cannon AB, Westropp JL, Ruby AL, Kass PH. JAVMA 231:570-576, 2007