Natriuria and calciuria levels in preeclampsia: a cross-sectional study

CONTEXT AND OBJECTIVE

Sodium excretion abnormalities in preeclampsia have been studied in relation to several factors. The objective of this study was to compare natriuria (mEq/24 h) and calciuria levels (mg/24 h) in preeclamptic patients.

DESIGN AND SETTING

An analytical cross-sectional study with a control group was conducted in the obstetric center and the high-risk pregnancy outpatient clinic at a university hospital in southern Brazil, and in a primary healthcare unit in the same city, including pregnant women with mild preeclampsia, severe preeclampsia or chronic hypertension, and women with normal pregnancies (14 patients in each group).

METHOD

Natriuria was measured using an ion-selective electrode in an automated clinical chemistry analyzer (Hitache 917, Roche). All the patients collected 24-hour urine, at home or at the hospital, for analysis of proteins, creatinine, calcium, sodium and uric acid. Quantitative variables with asymmetrical distribution were described using the median, minimum and maximum, and were compared using the Kruskal-Wallis test. The results were logarithmically transformed, with one-way analysis of variance (ANOVA) by ranks and then the post-hoc Tukey test, and were analyzed by means of the Spearman correlation and receiver operating characteristic (ROC) curve. The significance level used was 0.05.

RESULTS

There were significant differences between the groups in comparing severe preeclampsia with chronic hypertension and severe preeclampsia with controls (P < 0.0001 for both measurements).

CONCLUSION

Natriuria levels may be lower in preeclampsia when associated with calciuria. Natriuria assessment is an additional test for differential diagnosis of hypertensive diseases in pregnancy, but is a poor predictor when used alone.

Urinary protein/creatinine ratio in hypertensive pregnant women

OBJECTIVES

To determine the correlation between the protein/creatinine ratio and 24-h proteinuria; to estimate the sensitivity and specificity of this ratio for the diagnosis of significant proteinuria; to establish its cutoff point with the best predictive value for the diagnosis of significant proteinuria in patients with systemic arterial hypertension.

STUDY DESIGN

A cross-sectional study of 47 hypertensive patients who had been pregnant for 20 weeks or more seen at the Maternity of the University Hospital of Porto Alegre. The studied factor was the protein/creatinine ratio measured in a single random urine sample and the outcome was protein determination in 24-h urine. The level of significance was set at 0.05.

RESULTS

The correlation coefficient between the protein/creatinine ratio and 24-h proteinuria was 0.94 when urine was properly collected. A receiver-operator characteristic curve was constructed to determine the sensitivity and specificity of the ratio for the diagnosis of significant proteinuria (> or = 300 mg in 24 h). Specificity and predictive positive value were 100% for a ratio > or = 0.8. The best values for sensitivity, specificity, positive predictive value, and negative predictive value in the diagnosis of proteinuria > or = 300 mg in 24 h were obtained when the protein/creatinine ratio was 0.5 (0.96, 0.96, 0.96, and 0.96, respectively).

CONCLUSION

The protein/creatinine ratio measured in a single urine sample taken at random from hypertensive pregnant women showed good sensitivity and specificity for the diagnosis of 24-h proteinuria > or = 300 mg and was strongly correlated with 24-h proteinuria. A ratio of 0.5 mg/mg is predictive of significant proteinuria and can be used for the diagnosis and follow-up of hypertensive pregnant women.

Calciuria and preeclampsia

Urinary calcium excretion has been reported to be diminished in preeclampsia. The objective of the present study was to determine urinary calcium excretion in pregnant patients with chronic arterial hypertension (CAH) and preeclampsia (PE), and in normotensive patients (N). Forty-four pregnant patients (gestational age, 20-42 weeks; 18 CAH, 17 PE, 9 N) were evaluated for calciuria, proteinuria, plasma uric acid and blood pressure. Patients with PE (82 +/- 15.1 mg/24 h) showed significantly lower calciuria (P < 0.05) than the group with CAH (147 +/- 24.9 mg/24 h) and the N group (317 +/- 86.0 mg/24 h) (P < 0.05, Student t-test). Plasma uric acid was significantly higher in the PE group (6.1 +/- 0.38 mg/dl) than the CAH group (5.0 +/- 0.33 mg/dl; P < 0.05), which also presented higher proteinuria levels, although the difference was not statistically significant. Diastolic and systolic blood pressure did not differ between the PE (164 +/- 105 mmHg) and CAH (164 +/- 107 mmHg) groups. Calciuria was significantly lower in the group with preeclampsia than in the group with chronic arterial hypertension. We conclude that calciuria can be a further factor for identifying preeclampsia.