The Impact of Body Mass Index on the Stone Composition of 191 Patients Who Received Percutaneous Nephrolithotomy in a Single Hospital

Objective: We aimed to analyze the renal stone composition and evaluate the epidemiology of body mass index (BMI) and renal stones. Materials and Methods: We conducted a retrospective, single-center study of patients with large stones (>2 cm) who underwent percutaneous nephrolithotomy for renal stones between 2010 and 2015. We performed stone analysis using stereomicroscopy and infrared spectroscopy to determine the chemical composition of these stones. Chi-square analysis was used to determine the relationship between BMI and renal stone formation. Results: We examined stones from 191 procedures. Among these stones, we classified 58.6% as having "pure" composition and 40.8% as having "mixed" composition. Most stones (68.1%) were composed of calcium oxalate monohydrate (COM), followed by carbonate apatite (50.8%), calcium oxalate dihydrate (COD) (36.6%), uric acid (14.1%), struvite (8.9%), ammonium hydrogen mate (2.1%), and brushite (1.0%). Chi-square analysis revealed that stones in obese patients (BMI >27 kg/m(2)) were more likely to contain COM (hazards ratio [HR]: 1.66, 95% confidence interval [CI]: 1.10-2.49, P = 0.008) and less COD (FIR: 0.77, 95% CI: 0.60-0.99, P = 0.049) than stones in nonobese patients (BMI <= 27 kg/m(2)). Conclusion: COM is the most frequently occurring compound in renal stones. Obese patients were significantly more likely to develop COM-containing renal stones. One must consider these factors when choosing a treatment modality.