Computerized Tomography Based Diagnosis of Visceral Obesity and Hepatic Steatosis is Associated with Low Urine pH

Purpose: Uric acid nephrolithiasis is associated with an elevated visceral fat area in kidney stone formers. Hepatic steatosis has also been linked to visceral obesity and nephrolithiasis. We evaluated the association of noncontrast computerized tomography based diagnosis of visceral obesity and hepatic steatosis with 24-hour urine parameters and stone composition in kidney stone formers. Materials and Methods: A total of 98 kidney stone formers were included in study who had computerized tomography imaging and 24-hour urine studies available. For each patient a single computerized tomography axial area measurement was obtained of the visceral fat area. Hepatic steatosis was diagnosed by comparing the HU of regions from the liver and spleen. Univariate analysis was performed to compare patients with or without an elevated visceral fat area and hepatic steatosis. Multivariate linear and logistic regression was done to assess for variables associated with 24-hour urine parameters and stone composition. Results: An elevated visceral fat area was associated with higher 24-hour urine sodium (175 vs 157 mg per day, p < 0.036) and lower 24-hour urine pH (5.724 vs 6.478, < 0.0001). Urine pH less than 6 (OR 2.52) was associated with hepatic steatosis. Low urine pH less than 6 (OR 11.1, p = 0.004) and stone volume greater than 65 mm 3 (OR 5.12, p = 0.023) were associated with an elevated visceral fat area. Low urine pH less than 6 (OR 5.87) and visceral fat area greater than 48% (OR 5.33) were associated with uric acid stones. Linear regression demonstrated that the percent of visceral fat area was associated with lower 24-hour urine pH (beta-coefficient -0.438, p < 0.0001). Conclusions: Noncontrast computerized tomography based diagnosis of visceral obesity is associated with low urine pH, high urinary sodium and uric acid stone formation. Hepatic steatosis is associated with low urine pH.