Obstetric Medicine > Volume 1, Number 1 > Pp. 18-23

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Original articles

A practical approach to using spot urine protein/creatinine ratios for assessing proteinuria in pregnancy

Catherine A Marnoch MB ChB FRACP   ^* , Lucia Larson MD   ^*, Sherry Weitzen MS PhD   , Maureen G Phipps MD MPH   , C James Sung MD FCAP    and Raymond O Powrie MD FRCP(C)   ^*

^* Department of Medicine; Division of Research, Department of Obstetrics and Gynecology and Community Health; Department of Pathology, Women and Infants Hospital of Rhode Island, Warren Alpert Medical School of Brown University, Providence RI, USA

Correspondence to: Dr Catherine Marnoch Email: catherine.marnoch{at}waitematadhb.govt.nz

Objective: The aim of this study is to assess the diagnostic accuracy of the spot urine protein/creatinine ratio compared with the 24-hour urine protein in pregnancy.

Study Design: In this prospective cohort study of inpatient pregnant women, the protein/creatinine ratio and dipstick protein were assessed from a single urine sample collected at the start of the 24-hour urine. Both tests were compared with the 24-hour urine protein for correlation and test characteristics.

Results: In the 196 specimens analysed, we found a strong correlation between the spot urine protein/creatinine ratio and 24-hour urine protein (r² = 0.78, P < 0.01). A protein/creatinine ratio <0.1 ruled out significant proteinuria (300 mg/day) with sensitivity and negative predictive value 100%. A protein/creatinine ratio 0.4 detected significant proteinuria (specificity and positive predictive value of 100%). A protein/creatinine ratio 4.6 had a specificity and positive predictive value of 100% for detecting severe proteinuria (5000 mg/day). Urine dipsticks correlated poorly with the 24-hour urine protein (r² = 0.40, P = 0.826). Nineteen percent of dipsticks reading nil or trace were false-negative results.

Conclusion: The spot urine protein/creatinine ratio correlated well with the 24-hour urine protein and performed better than the urine dipsticks. Significant proteinuria in pregnancy was excluded if the protein/creatinine ratio was <0.1 and identified when it was 0.4.

Key Words: pregnancy • proteinuria • protein/creatinine ratio • sensitivity • specificity

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