Correlation Between CT-Based Bone Mineral Density and Kidney Stone Size and Their Association with 24-Hour Urinalysis Biometrics in Patients with Urinary Stones

Background: The association between chronic nephrolithiasis and several systemic conditions has been established in previous studies. Patients with recurrent urinary stones generally experience more urinary calcium loss, resulting in a lower bone mineral density (BMD). Dual-energy X-ray absorptiometry (DEXA) is the standard imaging method for diagnosing a low BMD. However, imaging imposes significant cost and radiation burden on patients. Objectives: We aimed to assess the relationship between 24-hour urinalysis biometrics and bone mineral content, retrieved from non-contrast computed tomography (CT) imaging, which is routinely preformed for urinary stone patients as a primary evaluation. Patients and Methods: The sample population for this retrospective study included urinary stone patients, undergoing percutaneous nephrolithotomy (PCNL) during 2015-2019, with available 24-hour urinalysis and CT imaging records. Stone size was defined as the maximum stone diameter on the CT image. BMD for each subject was also calculated at the vertebral L1 level, with CT attenuation measured in Hounsfield units (HU). According to the literature, a cutoff value of 160 HU was selected to distinguish normal BMD from low BMD. Results: The present results showed a significant association between the stone size and BMD (P < 0.05). Moreover, patients with a low BMD had a higher urinary calcium excretion in the 24-hour urinalysis (P < 0.05). Evaluation of urine chemical composition and stone size demonstrated a significant association between hypercalciuria and urinary stone volume (P < 0.05). Conclusion: A low BMD detected by CT imaging in patients with urinary stones is associated with abnormal 24-hour urinalysis biometrics and larger stones; therefore, it should be properly assessed.