Albumin‐To‐Creatinine Ratio Underestimates True 24‐Hour Albuminuria in Obesity: Clinical Relevance for Vascular Risk Stratification

AIMS: Albuminuria is a recognized marker of endothelial dysfunction and early cardiovascular risk. The albumin-to-creatinine ratio (ACR) is widely used to estimate urinary albumin excretion, but in individuals with high fat-free mass (FFM), such as those with obesity, elevated urinary creatinine may lead to underestimation of albuminuria. We aimed to investigate the concordance between ACR and 24-h urinary albumin excretion (UAE) in adults with obesity and examine whether discrepancies affect the detection of vascular dysfunction. METHODS: 140 individuals affected by severe obesity were enrolled. Albuminuria was assessed using both spot ACR and 24-h UAE. A subgroup of 70 participants underwent vascular testing, including carotid-femoral pulse wave velocity (cf-PWV) and allometrically scaled flow-mediated dilation (FMD). Multivariable linear models were used to evaluate associations between albuminuria markers and vascular parameters, adjusting for age, sex, blood pressure, and HbA1c. RESULTS: 24h-UAE ≥ 30 mg was more frequent in males (35%) than females (20%), while ACR ≥ 30 mg/g showed no sex difference; 21 individuals (15%) exhibited elevated 24 h-UAE (≥ 30 mg/24 h) despite a normal ACR (< 30 mg/g), a discordant pattern predominantly observed in males with high FFM and urinary creatinine levels. Interestingly, both ACR and UAE were independently associated with reduced FMD (st.β = -0.27 and -0.24; p < 0.05). No sex-based interactions were observed in the vascular models. CONCLUSIONS: In individuals with obesity, ACR may underestimate albuminuria, especially in males. Despite this, both markers are associated with early endothelial dysfunction. UAE may provide added value in cardiovascular risk stratification where ACR underperforms.