12-Hour Urine Collection OK For Preeclampsia Diagnosis

A12-hour urine collection performs similarly to a 24-hour urine collection for the diagnosis of proteinuria in women with suspected preeclampsia, according to a study published in the October issue of Obstetrics & Gynecology. The shorter collection time maintains high sensitivity and specificity, with the added benefit of convenience and improved clinical efficiency, the authors say.

Quantification of urinary protein remains an important diagnostic step in the evaluation of hypertension during pregnancy in the absence of severe symptoms, including end organ involvement (thrombocytopenia, elevated liver transaminases, renal insufficiency, pulmonary edema, or new-onset neurologic symptoms).

“Several studies have investigated urine protein-to-creatinine ratio as a rapid test to obviate the need for a 24-hour urine collection,” write the authors led by Molly Stout, M.D., from Washington University in St. Louis, Mo. “Although the data show that extremely high or low urine protein-to-creatinine ratio values may be a substitute for a 24-hour urine collection, there are clinical circumstances that may still require a 24-hour urine collection.”

Dipstick quantification of urine protein is also not recommended, according to the American College of Obstetricians and Gynecologists.

The researchers conducted a literature search to identify studies that compared results of both the 12-hour and 24-hour urine collection in the same female patients (at or beyond 20 weeks of gestation). Test performance characteristics from each study were extracted and a diagnostic meta-analysis was performed to determine summary diagnostic characteristics and to estimate the optimal cut-off point for the diagnosis of proteinuria using the 12-hour urine collection. Proteinuria was defined as 300 mg of protein in 24 hours. Included studies must have reported total protein, not concentration.

Analysis was based on a total of seven studies that met inclusion criteria (410 patients). The incidence of 24-hour urine protein greater than 300 mg ranged from 14 percent to 86 percent in the studies. There was also variation in the cut-off point used for a positive 12-hour urine collection, ranging from 100 to 165 mg.

The researchers found that 12-hour urine protein was overall “highly predictive” of proteinuria (area under receiver operating characteristic curve: 0.97). The optimal cut-off point was 150 mg of protein on 12-hour collection, which maximized sensitivity and minimized false-positives. Using this cut-off, the pooled sensitivity was 92 percent and specificity was 99 percent.

The authors note that while future study should evaluate standardization of collection (bed rest, day versus night), use of the 12-hour urine collection would be more convenient and expedite diagnosis and clinical management, and decrease cost.

Takeaway: Metabolomic profiles in serum may be useful in screening women for early- stage ovarian cancer. While further validation in larger populations is necessary, the researchers say a clinical assay based on the 16 markers is technically feasible.