Correlation of random urine protein creatinine (P-C) ratio with 24-hour urine protein and P-C ratio, based on physical activity: a pilot study

Quantification of proteinuria is usually predicated upon 24-hour urine collection. Multiple factors influence urine collection and the rate of protein and creatinine excretion. Urine collection is often incomplete, and therefore creatinine and protein excretion rates are underestimated. A random urine protein-creatinine (P-C) ratio has been shown over the years to be a reliable alternative to the 24-hour collection for detection and follow up of proteinuria. However, urine protein excretion may be influenced by physical activity. We studied 48 patients with proteinuria and varying levels of physical activity to determine the correlation between the measures of urine protein excretion. The correlation coefficient (r) between 24-hour urine total protein and random urine P-C ratio was 0.75 (P < 0.01) in the overall study population, but varied according to the level of proteinuria and physical activity in a stratified analysis: r = 0.99 (P < 0.001) and r = 0.95 (P < 0.01) in bedridden patients; r = 0.44 (P = not significant [NS]) and r = 0.54 (P = NS) in semiactive patients; and r = 0.44 (P = NS) and r = 0.58 (P < 0.05) in active patients with nephrotic- (>3500 mg/day) and non-nephrotic (<3500 mg/day) range proteinuria, respectively. The correlation appeared to be stronger between random urine and 24-hour urine P-C ratio for the overall study population (r = 0.84; P < 0.001), and when stratified according to the level of proteinuria and physical activity: r = 0.99 (P < 0.001) and r = 0.92 (P < 0.01) in bedridden patients; r = 0.61 (P = NS) and r = 0.54 (P = NS) in semiactive patients; and r = 0.64 (P < 0.02) and r = 0.52 (P < 0.05) in active patients with nephrotic and non-nephrotic range proteinuria, respectively. We conclude that the random urine P-C ratio is a reliable and practical way of estimating and following proteinuria, but its precision and accuracy may be affected by the level of patient physical activity.