Characterizing the Clinical, Vascular, and Functional Phenotype of Metabolic Acidosis in Kidney Transplantation: A Cross-Sectional Study

<b>Introduction</b>: Metabolic acidosis is common after kidney transplantation and is associated with adverse outcomes. However, its vascular and functional correlates in kidney transplant recipients remain insufficiently characterized. <b>Methods:</b> We conducted a cross-sectional study of adult kidney transplant recipients attending routine outpatient visits at a tertiary transplant center. Metabolic acidosis was defined as serum bicarbonate < 22 mmol/L. Arterial stiffness was assessed by carotid-femoral pulse wave velocity (PWV), and physical frailty was evaluated using the Fried frailty phenotype. Multivariable regression models were used to identify determinants of metabolic acidosis and to examine its association with arterial stiffness and frailty severity. <b>Results:</b> Among 239 patients (median age 46 years), 154 (64%) had metabolic acidosis. Lower estimated glomerular filtration rate and higher systemic inflammation were independently associated with metabolic acidosis. Metabolic acidosis was independently associated with higher arterial stiffness, with a 1.41 m/s higher PWV after adjustment for age, sex, blood pressure, kidney function, and diabetes mellitus (<i>p</i> < 0.001). Although metabolic acidosis was associated with greater frailty severity in minimally adjusted models, this association was attenuated and no longer statistically significant after further adjustment for kidney function, diabetes, and inflammation. In stable kidney transplant recipients, metabolic acidosis is independently associated with increased arterial stiffness but not with frailty after accounting for key clinical confounders. <b>Conclusions:</b> These findings highlight metabolic acidosis as a marker of vascular vulnerability and a potential therapeutic target after kidney transplantation.