The accuracy of spot urinary protein-to-creatinine ratio in confirming proteinuria in pre-eclampsia

Background: The gold standard for diagnosis of proteinuria in pre-eclampsia is traditionally a 24-h urine collection. Current Australian guidelines advocate use of the spot urine protein-to-creatinine ratio (PCR); however, there is controversy in the international literature about its accuracy and little recent Australian data exists. Aim: To clarify the accuracy of the spot urine PCR in a cohort of Australian women with pre-eclampsia. Methods: Women with pre-eclampsia over a 52-month period from a single obstetric unit were included in the study. Spot urine PCR, 24-h urine collection, gestation at delivery, severe hypertension in labour and magnesium sulphate requirement were recorded. Primary analysis of predictive values was performed on women who had had both a spot urine PCR and a 24-h collection. Continuous data were assessed using least squares analysis with Pearson correlation coefficient, Bland-Altman plot and receiver operator characteristics curve. Results: Two hundred and seventeen women had pre-eclampsia, and 121 of these underwent both tests. The two tests were highly correlated (r = 0.98, P < 0.0001). The urine PCR had a positive predictive value of 94% and a sensitivity of 95% for predicting proteinuria. There were no significant increases in the diagnosis of severe hypertension in labour nor the need for magnesium sulphate infusion in labour in those women in whom the 24-h collection was omitted. Conclusions: The urine PCR is highly accurate in predicting significant proteinuria in women with pre-eclampsia using the recommended cut-off of 30 mg/ mmol. Our findings support current guidelines suggesting the use of a 24-h urine collection is now rarely required.