Urine Albumin-creatinine Ratio Accurately Reflects Daily Albuminuria in Nonobese Patients but Requires Body Weight Correction in Obese.

Abstract

Objective: Urine albumin-creatinine ratio (UACR) is widely used to estimate daily albuminuria. Despite efforts to improve the accuracy of the estimated albumin excretion rate, the individual contributions of age, sex, and body weight remain unexplored.

Methods: This hospital-based cohort study examined the explanatory power of various factors and compared total R² values across different sets of factors to determine the optimal estimated albumin excretion rate model.

Results: An analysis of 304 24-hour urine samples revealed a median value of 0.538 g (interquartile range: 0.091-2.080 g), identifying UACR and body weight as significant factors with high partial R² values in estimating daily albuminuria. A novel model using only UACR and body weight demonstrated performance comparable to previous models that included additional variables (total R² values: ours 0.922 vs. 0.923, P = .893; ours 0.922 vs. 0.925, P = .727), and outperformed the model that excluded body weight (total R² values: ours 0.922 vs. 0.855, P < .001). Receiver operating characteristic analysis identified 78.1 kg (body mass index [BMI] of 28.5 kg/m²) as the optimal cutoff for predicting underestimation of daily albuminuria by UACR in the heavier half of our patient cohort (area under the curve: 0.865). For individuals with body weight less than 78.1 kg (0th-75.4th percentile), daily albuminuria (g) could be estimated as: 0.033 + 0.999 × UACR (mg/mg) (total R²: 0.966). Conversely, for those weighing ≥78.1 kg (75.5th-100th percentile), the estimation formula was as follows: -3.885 + 1.538 × UACR (mg/mg) + 0.045 × body weight (kg) (total R²: 0.942).

Conclusions: For individuals with a BMI below 28.5 kg/m², the UACR alone provides sufficient accuracy for estimating daily albuminuria (using the formula: daily albuminuria (g) = 0.033 + 0.999 × UACR (mg/mg)). However, for those with a BMI of 28.5 kg/m² or higher, adding body weight as a single correction factor to UACR sufficiently improves the explanatory power, simplifying clinical practice by eliminating the need for age and sex as additional factors.