Urinary Cystine/Creatinine Concentrations Before and After Castration in Dogs With Suspected Androgen‐Dependent Cystine Urolithiasis

ABSTRACT Background Androgen‐dependent cystinuria has been described in intact male dogs. Castration has been recommended to reduce urinary cystine excretion. Hypothesis/Objectives Urinary cystine/creatinine concentration will significantly decrease in dogs with suspected androgen‐dependent (Type III) cystinuria after castration and will be associated with a lack of sonographic evidence of urolithiasis. Animals Six intact male dogs with cystine uroliths. Methods Prospective, observational study. Urinary amino acid/creatinine concentrations and abdominal ultrasound were evaluated at baseline (T0), 30 days (T30), and 90 days (T90) after castration and urolith removal. No dietary change was recommended unless urolith recurrence was noted. DNA was evaluated for the cystinuria‐associated marker for Type III cystinuria. Results The median decline in urinary cystine/creatinine (uCys/creat) concentration from T0 to T30 was 577 nmol/mg (IQR, 415–969; p = 0.03), from T0 to T90 was 798 nmol/mg (IQR, 580–989; p = 0.03) and from T30 to T90 was 34 nmol/mg (IQR, 19.5–443; p = 0.03). Two dogs had small (2.5–3 mm) uroliths at T30, which resolved in one of them at T90. Both dogs with ultrasonographic evidence of recurrence at T30 were positive for the cystinuria‐associated genetic marker, although no signs of lower urinary tract disease were noted in either dog. Three of 6 enrolled dogs were homozygous positive for the genetic marker. Conclusions and Clinical Importance Castration should be considered for intact male dogs with cystine urolithiasis.