Does bladder stone composition predict kidney stone composition?

INTRODUCTION Bladder stones have historically been associated with urinary stasis secondary to bladder outlet obstruction (BOO). Recent studies indicate that the role of BOO in bladder stone formation is minor. We evaluate the role of urinary lithogenic factors in bladder stone formation by comparing the compositions of bladder stones and kidney stones in patients with multi-site urinary calculi. MATERIALS AND METHODS: We identified patients who were treated for concomitant bladder stones and kidney stones between 2008-2019, and had both stone compositions available. Patients with bladder stone size < 10 mm, urinary foreign bodies, encrusted stents or tumors were excluded. Data regarding urinary symptoms, residual volumes, stone composition and 24-hours urine data were collected. RESULTS: We identified 40 males with a median age of 72 years (IQR 6-14), median residual volume of 76 mL (IQR 41-200), and a median prostate volume of 52 mL (IQR 32-102). Bladder outlet procedures were performed concomitantly with cystolitholapaxy in 21 (53%) patients. The most common bladder stone and kidney stone compositions were CaOx (47.5% and 65%), uric acid (32.5% and 22.5%), calcium phosphate (15% and 10%), and struvite (5% and 2.5%), respectively. Bladder stone and kidney stone compositions were identical in 70% of patients. Bladder stone composition was predictive of kidney stone composition, regardless of the PVR, bladder stone size, or whether an outlet procedure was performed. CONCLUSION: We found a high concordance between bladder stone and kidney stone composition, suggesting that metabolic abnormalities have a significant role in bladder stone formation. Bladder stone composition can be used to guide surgical and medical treatment for kidney stones in metabolically active stone patients.