Variation in the Urinary Protein/Creatinine Ratio at Four Different Periods of the Day in Hypertensive Pregnant Women

The value of the urinary protein:creatinine ratio for the detection of significant proteinuria in women with suspected preeclampsia

To explore the correlation between urinary protein:creatinine ratio and 24-h excretion of protein, we studied 149 women referred to a day assessment unit for investigations for suspected preeclampsia. Paired samples were obtained for measurement of urinary protein:creatinine ratio and 24-h protein excretion. Collection of a 24-h urine sample was validated by the daily creatinine excretion. The outcome measure was proteinuria of 300 mg/day or more. Inaccurate 24-h collection was observed in 17% of women. All women (n = 56) with a protein:creatinine ratio >60 mg/mM had significant proteinuria. No woman with protein:creatinine ratio <18 mg/mM (n = 20) had significant proteinuria. We recommend that a dual cut-off should be used for excluding and "ruling in" the diagnosis of significant proteinuria. A 24-h urine collection should be used only for urinary protein:creatinine ratio values between 18 and 60 mg/mM in the detection of significant proteinuria.

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

OBJECTIVE

To 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.

DESIGN

Prospective study.

SETTING

Tertiary referral university centre.

POPULATION

Women suspected of having pre-eclampsia, admitted to the Erasmus Medical Centre.

METHODS

Twenty-four-hour urine collections and simultaneously three single voided 5-ml aliquots were obtained at 8 a.m., 12 a.m. (noon) and 5 p.m. A PCR was measured in each specimen and compared with the 24-hour protein excretion.

MAIN OUTCOME MEASURES

The 24-hour proteinuria and PCR measured in spontaneous voids.

RESULTS

The 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 0.3 g protein per 24-hour had an area under the curve of respectively 0.94 (8 a.m.), 0.96 (noon) and 0.97 (5 p.m.). Sensitivities at 8 a.m., noon and 5 p.m. were respectively 89%, 96% and 94%; specificities were 75%, 78% and 78% with the proposed PCR cut-off of 30 mg/mmol (0.26 g/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.

CONCLUSION

The 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.

Diagnosis, evaluation, and management of the hypertensive disorders of pregnancy

OBJECTIVE

This guideline summarizes the quality of the evidence to date and provides a reasonable approach to the diagnosis, evaluation and treatment of the hypertensive disorders of pregnancy (HDP).

EVIDENCE

The literature reviewed included the previous Society of Obstetricians and Gynaecologists of Canada (SOGC) HDP guidelines from 2008 and their reference lists, and an update from 2006. Medline, Cochrane Database of Systematic Reviews (CDSR), Cochrane Central Registry of Controlled Trials (CCRCT) and Database of Abstracts and Reviews of Effects (DARE) were searched for literature published between January 2006 and March 2012. Articles were restricted to those published in French or English. Recommendations were evaluated using the criteria of the Canadian Task Force on Preventive Health Care and GRADE.

Proteinuria in special populations: pregnant women and children

Proteinuria is the hallmark of glomerular kidney disease. It is used diagnostically to follow disease progression and to determine response to therapy. Thus, it is necessary to have an understanding of the mechanisms of proteinuria and the limitations to its accurate assessment in special populations. In this article, we review 2 special populations--pregnant women and children--providing insight into their unique circumstances that require consideration when assessing proteinuria.

Protein creatinine ratio in random urine sample of hypertensive pregnant women: maternal and perinatal outcomes

Objective. To compare protein/creatinine ratio (PCR) in random urine sample levels and adverse outcomes in hypertensive pregnant women. Methods. A total of 370 medical charts from hypertensive pregnant women were reviewed and stratified into three groups according to different PCR in random urine sample levels (group 1: PCR < 0.3 mg/mg; group 2: PCR 0.3-1.99 mg/mg; group 3: PCR ≥ 2.0 mg/mg) and compared with composite maternal and perinatal outcomes. Those outcomes were severe hypertension, thrombocytopenia, high lactate dehydrogenase count, disseminated intravascular coagulation, abruptio placentae, HELLP (hemolysis, elevated liver enzymes, low platelet count) syndrome, eclampsia, perinatal death, newborn cerebral hemorrhage, respiratory distress syndrome of newborn, neonatal sepsis, and newborn small for gestational age. Results. To obtain a composite maternal adverse outcome the odds ratio [ORs] between PCR groups were 1.8 (95% confidence interval [CI]: 1.1-3.2) between groups 1 and 2, and 3.1 (95% CI: 1.5-6.3) between groups 1 and 3; for composite perinatal adverse outcomes, the ORs were 3.0 (95% CI: 1.5-5.9) between groups 1 and 2, and 3.4 (95% CI: 1.6-7.5) between groups 1 and 3. Conclusions. Hypertensive pregnant women with a PCR ≥ 0.3 mg/mg, had worse maternal and perinatal outcomes than those with PCR < 0.3 mg/mg. Above the cut-off of 0.3 mg/mg, higher PCRs are not associated with a significant increase in maternal and perinatal morbidity.

Urinary copper/zinc ratio: a promising parameter for replacement of 24-hour urinary copper excretion for diagnosis of Wilson's disease in children

BACKGROUND

Although 24-hour urinary copper excretion is valuable for diagnosis of Wilson's disease, accurate, timed collection entails practical difficulties. This study aimed to investigate the feasibility of morning urinary copper/creatinine or copper/zinc ratio as replacement parameter for diagnosing Wilson's disease.

METHODS

Five random urinary samples collected during 24 hours from two inpatients were used to estimate the consistency of urinary copper/creatinine and copper/zinc ratios. The correlation of the ratios with 24-hour urinary copper excretion was studied in 15 patients with liver diseases. The diagnostic value of morning urinary copper/zinc ratio was further studied in 9 children with Wilson's disease and 22 children with other liver diseases.

RESULTS

The coefficients of variation of urinary copper/creatinine and copper/zinc ratios during 24 hours were 12.5% and 9.3% respectively. The morning urinary copper/creatinine ratio, copper/zinc ratio, and 24-hour urinary copper excretion were correlated well. The area under receiver-operating characteristic curve was comparable between the morning urinary copper/zinc ratio and 24-hour urinary copper excretion (0.983 vs. 0.977).

CONCLUSION

Morning urinary copper/zinc ratio seems to be a promising parameter in replacement of 24-hour urinary copper excretion for diagnosis of Wilson's disease.

Interpreting abnormal proteinuria in pregnancy: the need for a more pathophysiological approach

This review and opinion article focuses on the definitions and meanings of abnormal protein excretion in pregnancy, asking the following questions: Are our tests to determine abnormal proteinuria adequately performed? Are current guidelines for diagnosis of excessive proteinuria, especially when used to identify preeclampsia, supported by adequate data? Can the magnitude of proteinuria be used as a reliable clinical biomarker of the gravity of preeclampsia? Should timed urine collections, primarily 24-hour excretions, be supplanted by the urine protein/creatinine ratio in clinical practice? The answers to most of these questions are: We are not sure, or some guidelines are poorly supported by data and may prove erroneous. We suggest a more physiologic approach to assessment of proteinuria and believe that if clinicians and investigators looked at proteinuria in terms of how the kidney handles protein in health and disease it would lead to a more rational and evidence-based approach to proteinuria in pregnancy. Finally, we recommend that current cutoff for abnormal proteinuria be used to diagnose preeclampsia, but the level of proteinuria should not guide management. Other variables, such as status of blood pressure control, evidence of increasing organ damage in the liver and hematological systems, evidence of falling glomerular filtration rate, and signs of neurological involvement, are more reliable indicators of severity of preeclampsia.

PROTEINURIA IN PREECLAMPSIA: FROM BENCH TO BEDSIDE

Pre-eclampsia (PE) remains the leading cause of maternal and fetal mortality in the developed world and parts of the developing world. Morbidity and mortality from PE is increased in the developing world compared to the developed world, as availability and access to antenatal care and pathology services are limited.

Protein and albumin-to-creatinine ratios in random urines accurately predict 24 h protein and albumin loss in patients with kidney disease

BACKGROUND

Random urine protein-to-creatinine (PCR) and albumin-to-creatinine (ACR) ratios have been proposed as alternatives to 24 h urine measurements to simplify sample collection and overcome errors. The aim of this study was to examine the ability of PCR and ACR to predict urinary 24 h protein and albumin loss, respectively, in patients with kidney disease, and determine the most appropriate time of collection.

METHODS

Eighty-three patients were recruited from a renal outpatient clinic. In a 24 h period, each collected an early-morning urine (EMU), second and third voids, and the remaining urine passed that day. PCR and ACR were determined in random urines and compared with the 24 h loss of protein and albumin, respectively.

RESULTS

For all patients, median (range) 24 h urine protein and albumin losses were 220 (30-15600) and 60 (<8-10,557) mg, respectively. Ratios derived from each of three random urines correlated well with 24 h protein or albumin loss (Spearman's r(s) > 0.87, P < 0.0001). Receiver operator characteristic (ROC) curve analysis showed PCR accurately predicted both an abnormal 24 h urine protein > or =150 mg/24 h (areas under curves [AUC] 0.90-0.92) and significant proteinuria above 300 mg/24 h (AUC between 0.97 and 1.00). ACR accurately predicted both an abnormal 24 h urine albumin > or =30 mg/24 h (AUC 0.98 to 0.99) and frank albuminuria at > or =300 mg/24 h or > or =700 mg/24 h (AUC between 0.99 and 1.00). EMU and random urines performed equally well in predicting proteinuria and albuminuria from PCR and ACR, respectively.

CONCLUSIONS

By careful choice of cut-offs, both PCR and ACR can be used in patients with kidney disease to rule in or rule out abnormal 24 h losses of protein and albumin. EMU and, importantly, random samples can be used as surrogates for 24 h urine collections.

The 24-hour urine collection: gold standard or historical practice?

OBJECTIVE

The objective of the study was to determine completeness of 24-hour urine collection in pregnancy.

STUDY DESIGN

This was a retrospective laboratory/chart review of 24-hour urine collections at British Columbia Women's Hospital. Completeness was assessed by 24-hour urinary creatinine excretion (UcreatV): expected according to maternal weight for single collections and between-measurement difference for serial collections.

RESULTS

For 198 randomly selected pregnant women with a hypertensive disorder (63% preeclampsia), 24-hour urine collections were frequently inaccurate (13-54%) on the basis of UcreatV of 97-220 micromol/kg per day (11.0-25.0 mg/kg per day) or 133-177 micromol/kg per day (15.1-20.1 mg/kg per day) of prepregnancy weight (respectively). Lean body weight resulted in more inaccurate collections (24-68%). The current weight was frequently unavailable (28%) and thus not used. For 161 women (81% proteinuric) with serial 24-hour urine levels, a median [interquartile range] of 11 [5-31] days apart, between-measurement difference in UcreatV was 14.4% [6.0-24.9]; 40 women (24.8%) had values 25% or greater, exceeding analytic and biologic variation.

CONCLUSION

Twenty-four hour urine collection is frequently inaccurate and not a precise measure of proteinuria or creatinine clearance.

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

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 (r (2) = 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 (r (2) = 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.

Protein:creatinine ratio in random urine samples is a reliable marker of increased 24-hour protein excretion in hospitalized women with hypertensive disorders of pregnancy

BACKGROUND

The protein:creatinine ratio in random, untimed urine samples correlates with 24-h protein excretion in pregnant women with and without hypertension. Nevertheless, whether this ratio is appropriate as a screening test for proteinuria is still unclear, in part because of the paucity of large studies.

METHODS

We measured protein:creatinine ratios in random urine samples and protein contents of 24-h urine samples in a cross-sectional study of 927 hospitalized pregnant women at >/=20-weeks of gestational age and in a 2nd cohort of 161 pregnant women. In the 2nd group, urine specimens were obtained before and after completion of the 24-h collections, avoiding 1st-morning void specimens.

RESULTS

Protein excretion was >/=300 mg/24 h in 282 patients (30.4%). The urine protein:creatinine ratio and the 24-h protein excretion were significantly correlated (r = 0.98, P <0.001). The protein:creatinine ratio as an indicator of protein excretion >/=300 mg/24 h was >/=0.3. The sensitivity and specificity were 98.2% and 98.8%, respectively. Positive and negative predictive values were 97.2% and 99.2%, respectively, and positive and negative likelihood ratios were 79.2 and 0.02, respectively. The diagnostic accuracy of the urinary protein:creatinine ratio was corroborated in the 2nd cohort of patients, which also showed no statistically significant difference in protein:creatinine ratio between samples obtained >24 h apart.

CONCLUSIONS

Random urinary protein:creatinine ratio is a reliable indicator of significant proteinuria (>300 mg/day) in nonambulatory pregnant women, irrespective of sampling time during the daytime. The protein:creatinine ratio may be reasonably used as an alternative to the 24-h urine collection method.

Predicting proteinuria in hypertensive pregnancies with urinary protein-creatinine or calcium-creatinine ratio

OBJECTIVE

Evaluate the value of random urinary protein-creatinine (PrCr) and calcium-creatinine (CaCr) ratios to predict 24-h proteinuria in hypertensive pregnancies.

STUDY DESIGN

Spot urine samples were collected before routine 24-h urine collections from consecutive pregnant women with hypertension (n=83). Reliability of spot urinary PrCr and CaCr to detect significant proteinuria (>or=300 mg/day) using 24-h urine protein as 'gold-standard' was assessed by receiver-operating characteristic (ROC) curve.

RESULTS

Fifty-one patients (61.4%) had significant proteinuria (45 pre-eclampsia, 5 superimposed pre-eclampsia, 1 renal hypertension). Area under ROC curve to predict proteinuria was 0.82 (95% confidence interval (CI) 0.73 to 0.92, P<0.001) for PrCr and 0.55 (95% CI 0.43 to 0.68, P=0.2) for CaCr. A cutoff value of >0.19 for PrCr best predicted significant proteinuria with sensitivity, specificity, positive and negative predictive values and likelihood ratios (positive and negative), respectively, of 80.4, 68.8, 80.4, 68.8%, 2.57 and 3.51.

CONCLUSION

Spot urinary PrCr predicts total urinary protein excretion in hypertensive pregnancies.