Diagnostic Value of an 8-Hour Urine Protein Measurement in Preeclampsia

Background: Prompt diagnosis of preeclampsia in pregnant patients with new-onset hypertension is critical, and shorter urine collection intervals may offer a practical alternative to 24-hour urine testing for detecting proteinuria.To evaluate the predictive value and clinical utility of 8-hour urine samples for the diagnosis of preeclampsia, using 24-hour urine collection as the gold standard for detecting proteinuria in pregnant patients with new-onset hypertension. Methods: This prospective study enrolled 99 pregnant women with new-onset hypertension, defined as blood pressure ≥140/90 mmHg on two occasions at least 4 hours apart after 20 weeks of gestation, between December 2022 and April 2023 at the Obstetrics and Gynecology Clinic of Istanbul Training and Research Hospital. Participants were consecutively recruited before confirmation of proteinuria to reflect real-world diagnostic challenges in distinguishing gestational hypertension from preeclampsia. Patients were evaluated based on protein levels in their 24-hour urine samples, which served as the gold standard, and these values were compared with protein levels obtained from three consecutive 8-hour urine collections. Results: The mean age was 29.7 ± 6.0 years, and the mean gestational age was 33.5 ± 4.2 weeks. Based on the area under the curve (AUC), proteinuria measured in urine collected between 8 AM and 4 PM demonstrated the highest diagnostic accuracy for preeclampsia (AUC = 0.95). All 8-hour urine collections showed a statistically significant strong positive correlation with the 24-hour gold standard. Optimal cut-off values for 8-hour urine protein excretion for the diagnosis of preeclampsia were as follows: >121 mg/8 hours (8 AM to 4 PM), >81 mg/8 hours (4 PM to 12 AM), and >71 mg/8 hours (12 AM to 8 AM). Conclusion: Prompt diagnosis is critical in patients with new-onset hypertension during pregnancy. Our findings demonstrate that 8-hour urine protein measurement, particularly the 8 AM to 4 PM collection, provides a reliable alternative to 24-hour urine collection for detecting significant proteinuria in this population, offering a practical approach to expedite preeclampsia diagnosis and improve patient compliance.