Variation of urinary protein to creatinine ratio during the day in women with suspected pre-eclampsia

ObjectiveTo investigate the stability throughout the day of the protein to creatinine ratio (PCR) in spot urine, to demonstrate whether the PCR is a valid alternative for 24-hour protein investigation in pregnant women. DesignProspective study. SettingTertiary referral university centre. PopulationWomen suspected of having pre-eclampsia, admitted to the Erasmus Medical Centre. MethodsTwenty-four-hour urine collections and simultaneously three single voided 5-ml aliquots were obtained at 8a.m., 12a.m. (noon) and 5p.m. A PCR was measured in each specimen and compared with the 24-hour protein excretion. Main outcome measuresThe 24-hour proteinuria and PCR measured in spontaneous voids. ResultsThe PCRs correlated strongly with each other and with the 24-hour protein excretion but did show variation throughout the day (mean coefficient of variation 36%; 95% confidence interval 31-40%). The coefficient of variation was unrelated to the degree of 24-hour proteinuria. Receiver operating characteristics curves to discriminate between values below and greater than or equal to the threshold of 0.3g protein per 24-hour had an area under the curve of respectively 0.94 (8a.m.), 0.96 (noon) and 0.97 (5p.m.). Sensitivities at 8a.m., noon and 5p.m. were respectively 89%, 96% and 94%; specificities were 75%, 78% and 78% with the proposed PCR cut-off of 30mg/mmol (0.26g/g) (National Institute for Health and Care Excellence guidelines).There is no evidence of a difference between the three measurement times regarding the sensitivities and specificities. ConclusionThe PCR determined in spot urine varies throughout the day but is a valid alternative for 24-hour urine collections in pregnant women. It is especially useful to rapidly identify clinically relevant proteinuria.