Comparison of 24-hour urinary protein and protein-to-creatinine ratio in women with preeclampsia

Objective

To compare the spot urine protein-to-creatinine (P/C) ratio and 24-hour urine protein excretion in pregnant women with preeclampsia and also to determine the best discriminator values of the spot P/C ratios for 300 mg and 2000 mg protein per 24 h.

Study design

Prospective study of 200 pregnant women with new onset hypertension at or greater than 140/90 mmHg after 20 weeks of gestation. Women were instructed to collect urine during a 24-hour period, and after the 24-hour urine sample collection was completed a mid-stream urine specimen was obtained for P/C ratio determination. The correlation between 24-hour urine protein excretion and spot urine P/C ratio was calculated. The receiver operating characteristic (ROC) curve was used to identify the cut-off values of the spot P/C ratios for 300 mg and 2000 mg protein per 24 h. Areas under ROC curves were calculated.

Results

There was a significant correlation between 24-hour protein excretion and the urine P/C ratio (r = 0.828, p < 0.0001). The cut-off P/C ratio for 300 mg per 24 h was 0.28: sensitivity and specificity were 60.4% and 77.9%, respectively. The positive predictive value (PPV) was 77.5% and negative predictive value (NPV) was 60.9%. The cut-off P/C ratio for 2000 mg per 24 h was 0.77: sensitivity and specificity were 96.8% and 98.6%, respectively. The PPV was 96.8% and NPV was 98.6%. Area under ROC curves for 24-hour urine total protein of 300-2000 mg/day and >2000 mg/day were 0.74 (95% CI 0.66-0.80) and 0.99 (95% CI 0.95-0.99), respectively.

Conclusions

Spot P/C ratio is a poor predictor of 24-hour proteinuria but can predict proteinuria >2000 mg better than 300-2000 mg.