Correlation of Midday and Morning Urine Protein-Creatinine Ratio with 2 4-Hour Urine Protein

Background: Proteinuria is a key marker for diagnosing and monitoring chronic kidney disease (CKD) and is associated with disease progression and cardiovascular risk. Spot urine protein-to-creatinine (P/C) ratio offers a simpler alternative to 24-hour urine collection, but its accuracy remains debated. Objective: To evaluate the correlation between morning and midday spot P/C ratios and 24-hour urinary protein excretion and assess their diagnostic reliability.
Patients and Methods: In this cross-sectional study, 200 participants were scheduled for 24-hour urine protein estimation provided morning and midday spot urine samples for P/C ratio measurement. Demographic, anthropometric, biochemical, lipid profile, and urinalysis data were collected. Pearson correlation tested agreement between methods, and associations with lipid parameters were analyzed. Results: Mean ± standard deviation (SD) 24-hour urinary protein was 1.65 ± 1.38 mg, while morning and midday P/C ratios were 1.83 ± 2.2 mg/g and 1.72 ± 2.08 mg/g, respectively. Both morning (r = 0.783, P < 0.0001) and midday (r = 0.780, P < 0.001) P/C ratios showed strong positive correlations with 24-hour proteinuria, with closer agreement (P² = 0.9220) was according to multiple regression analysis. Significant positive correlations were, also, observed between 24-hour proteinuria and total cholesterol (P = 0.002), triglycerides (P = 0.006), and LDL cholesterol (P < 0.0001); similar correlations were found for morning and midday P/C ratios.
Conclusion: Morning and midday spot P/C ratios were strongly correlated with 24-hour urinary protein excretion. Midday sampling showed marginally superior agreement and, given its convenience, represents a practical and reliable alternative to 24-hour urine collection for assessing proteinuria and improving patient compliance without loss of diagnostic accuracy.