Association of plasma oxalate with computed tomography–derived stone characteristics in calcium oxalate nephrolithiasis

Calcium oxalate (CaOx) nephrolithiasis shows wide variation in stone size and density that is not fully explained by urinary risk factors. Plasma oxalate (POx) reflects systemic oxalate balance, but its relationship with imaging-defined stone characteristics has not been studied. We examined whether POx is associated with computed tomography (CT)–derived stone density and size in patients with CaOx stones. In this cross-sectional study, 80 adults with confirmed CaOx nephrolithiasis underwent clinical evaluation, laboratory testing, and non-contrast CT imaging. Stone density was measured in Hounsfield units (HU), and maximum stone diameter was recorded. Associations between POx, stone density, and stone size were evaluated using multivariable linear regression with HC3 robust standard errors adjusted for age, sex, estimated glomerular filtration rate (eGFR), body mass index, diabetes mellitus, disease duration, and the reciprocal stone characteristic. Higher log-transformed POx levels were associated with greater stone density (B = 196.2 HU, 95% CI 96.2–296.1; β = 0.400; p < 0.001). The association remained consistent after removal of stone size from the model (B = 186.9 HU, 95% CI 77.5–296.3; p = 0.001) and in analyses limited to participants with preserved kidney function (B = 218.0 HU, 95% CI 59.7–376.3; p = 0.008) and to patients with a single stone (B = 249.7 HU, 95% CI 97.7–401.7; p = 0.001). In patients with CaOx nephrolithiasis, higher POx levels were associated with greater CT-derived stone density. Prospective studies are required to determine the temporal and clinical implications of this association.