Proteinuria as a predictor of 24-hour albuminuria ≥30 mg in patients with lifestyle-related diseases

Background : Microalbuminuria is a risk factor for renal failure, cardiovascular diseases, and mortality in individuals with lifestyle-related diseases. Reports on the urine protein-to-creatinine ratio (uPCR) corresponding to a urine albumin-to-creatinine ratio (uACR) of 30 mg/gCr in spot urine have been inconsistent. Because both uACR and uPCR are influenced by muscle mass, this study aimed to determine whether 24-hour proteinuria can predict 24-hour albuminuria ≥30 mg using 24-hour urine collections. Methods : Japanese outpatients with lifestyle-related diseases (hypertension, diabetes, dyslipidemia, or hyperuricemia) who had uPCR <0.5 g/gCr and estimated glomerular filtration rate (eGFR) ≥15 mL/min/1.73 m ² were included. Patients with urine collection times within 1440 ± 144 min were analyzed. Twenty-four-hour albuminuria, proteinuria, and urinary salt excretion were calculated as: total urine values × 1440 (min)/actual collection time (min). The association between log-transformed 24-hour albuminuria and proteinuria was examined using a four-knot linear spline. ROC curve analysis determined cut-off values: CO(D), the shortest distance from (0, 1), and CO(YI), the maximum of (sensitivity + specificity – 1). Logistic regression identified predictors of 24-hour albuminuria ≥30 mg. Results : Median 24-hour albuminuria increased with higher 24-hour proteinuria in G1–4 (Adjusted R ² = 0.939, p <0.0001). The 24-hour proteinuria corresponding to a median 24-hour albuminuria of 30 mg was 78 mg. The CO(D) and CO(YI) of 24-hour proteinuria for detecting 24-hour albuminuria ≥30 mg were 47 mg and 52 mg, respectively, in G1–3a (area under the curve [AUC] 0.786) and 65 mg in G3b–4 (AUC 0.895, both p <0.0001). In G1–3a, hyperuricemia, higher body mass index, greater 24-hour urinary salt excretion, and lower calculated urinary osmolality were additional independent predictors of 24-hour albuminuria ≥30 mg. Incorporating these five factors increased the AUC to 0.838, providing greater predictive accuracy than 24-hour proteinuria alone (p <0.01). Conclusions : Prediction of 24-hour albuminuria ≥30 mg from 24-hour proteinuria was feasible. The cut-off values of 24-hour proteinuria for detecting 24-hour albuminuria ≥30 mg in Japanese outpatients with lifestyle-related diseases were 47 mg/day (CO[D]) and 52 mg/day (CO[YI]) in G1–3a, and 65 mg/day (CO[D], CO[YI]) in G3b–4. Trial registration : Prospectively registered.