title: The urinary protein-to-creatinine ratio in Canadian women at risk of preeclampsia: does the time of day of testing matter?
abstract: OBJECTIVE
  To determine the performance of a protein-to-creatinine ratio threshold of 30 mg/mmol in pregnant women investigated for hypertension according to the time of day of the sample.
  
  
  METHODS
  This prospective study included ambulatory pregnant women investigated for hypertensive disorders. A single voided random urine specimen was obtained to determine the protein-to-creatinine ratio, followed immediately by a 24-hour urine collection. Statistical analyses included Spearman correlation, sensitivity, specificity, predictive values, likelihood ratios, and receiver-operator characteristic curves with 95% confidence intervals. A P value < 0.05 was considered statistically significant.
  
  
  RESULTS
  Among the 91 specimens analyzed, 47.3% showed significant proteinuria in the 24-hour collection and 33% were first morning samples. The protein-to-creatinine ratio and 24-hour urinary protein excretion were highly correlated (r = 0.92, P < 0.001). The diagnostic accuracy of the protein-to-creatinine ratio threshold of 30 mg/mmol was lower in first morning samples than in samples obtained during the rest of the day, with sensitivity 58% and 90%, specificity 93% and 100%, positive predictive value 88% and 100%, negative predictive value 72% and 92%, positive likelihood ratio 8 and not calculable, and negative likelihood ratio 0.45 and 0.1, respectively. The receiver-operator characteristic area under the curve was 0.94 (95% CI 0.86 to 1) for first morning samples and 1.0 (95% CI 0.99 to 1) for other samples.
  
  
  CONCLUSIONS
  A protein-to-creatinine ratio threshold of 30 mg/mmol reliably identifies significant proteinuria, but its reliability is reduced in first morning samples. Consequently, such samples should not be used for this purpose.
authors.affiliation: Department of Obstetrics and Gynaecology, Cité de La Santé de Laval, Laval QC.
authors.forename: Annie
authors.initials: A
authors.lastname: Lamontagne
authors.affiliation: Department of Medicine, CHU Sherbrooke, Sherbrooke QC.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Côté
authors.affiliation: Department of Obstetrics and Gynaecology and Research Centre, CHU Sainte-Justine and Department of Medicine, University of Montreal, Montreal QC.
authors.forename: Evelyne
authors.initials: E
authors.lastname: Rey
mesh_terms: D000328:Adult; D003404:Creatinine / Q000652:urine*; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D011225:Pre-Eclampsia / Q000652:urine*; D011247:Pregnancy; D011446:Prospective Studies; D011507:Proteinuria / Q000175:diagnosis*; D012372:ROC Curve; D013997:Time Factors
chemical_list: D003404:Creatinine
keywords: diagnosis; hypertension; pregnancy; protein/creatinine ratio; proteinuria