Utility of Morning and Midday Spot Urine Protein–Creatinine Ratios in Predicting 24-Hour Proteinuria: A Clinical Review

Abstract

Background: Proteinuria is a key biomarker in the diagnosis, staging, and monitoring of kidney diseases, reflecting both glomerular integrity and tubular reabsorptive capacity. While the 24-hour urine protein measurement is traditionally regarded as the gold standard for quantifying proteinuria, it is inconvenient, prone to collection errors,and challenging for patient compliance. The spot urine protein-to-creatinine ratio (UPCR) has emerged as a reliable surrogate, offering simplicity, speed, and reproducibility. However, the timing of spot urine sampling particularly morning versus midday can influence protein excretion due to diurnal variations in renal hemodynamics, posture,dietary intake, and physical activity.