Urinary calcium in asymptomatic primigravidas who later developed preeclampsia

OBJECTIVE: To assess the efficacy of calciuria as a diagnostic test for the prediction of preeclampsia. METHODS: We asked young healthy primigravidas from the prenatal clinic in our hospital to collect a 24-hour urine sample at 17-20 weeks' gestation. Urinary calcium was measured and expressed as calciuria per 24 hours (mg/24 hours), urinary excretion of calcium per 24 hours on a basis of body weight (mg/kg/24 hours), and as the calciuria-creatinuria ratio (mg/mg). For each test, sensitivity, specificity, predictive values, and relative risk (RR) were calculated. The test with the best overall performance was determined by comparing receiver operating characteristic curves. Sixty-nine patients completed the study until the end of the puerperium, and 15 of them were diagnosed with preeclampsia. RESULTS: The most efficient test was the urinary excretion of calcium per 24 hours based on body weight. Using 3.4 mg/kg/24 hours as a cutoff point, we obtained a sensitivity of 80% (95% confidence interval [CI] 59.8-100), specificity 64.8% (95% CI 52.1-77.5), positive predictive value 38.7% (95% CI 21.6-55.8), negative predictive value 92.1% (95% CI 83.5-100), and RR 4.9 (95% CI 1.5-15.8). CONCLUSION: In young, apparently healthy primigravidas, a low urinary excretion of calcium per kilogram of body weight per 24 hours before the end of the first half of gestation is a risk factor for preeclampsia, with an acceptable sensitivity and high negative predictive value, but with a positive predictive value no better than chance.

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