Accuracy of 12-hour urine collection in the diagnosis of pre-eclampsia

To evaluate the accuracy of a 12-hour urine collection to diagnose pre-eclampsia and to determine whether time of collection influences the performance of this test.

A prospective observational study was conducted in a tertiary obstetric center in Portugal between November 1, 2015, and November 30, 2016. Pregnant women (≥20 weeks) admitted for observation with suspected pre-eclampsia were eligible for inclusion. Two consecutive 12-hour urine samples were collected (07:00-19:00 hours vs 19:00-07:00 hours). Protein levels were measured in each 12-hour sample, as well as in a pooled sample (07:00-07:00 hours). The diagnostic cut-off values for pre-eclampsia were 150 mg (12-hour samples) and 300 mg (24-hour sample).

The study included 99 patients and diagnoses of pre-eclampsia were confirmed among 42 (42%) patients. In all, 456 12-hour urine samples were analyzed (equivalent to 228 24-hour samples). Qualitative analysis (pre-eclampsia vs no pre-eclampsia) indicated substantial agreement between the 12- and 24-hour samples (Cohen κ 0.779). The sensitivity was 85.9% (95% confidence interval [CI] 81%-90%) and the specificity was 91.7% (95% CI 88%-95%). No statistically significant difference was found between the two 12-hour collections.

The 12-hour test showed acceptable accuracy for detecting pre-eclampsia, regardless of the time of collection.