The 24-hour urine collection: gold standard or historical practice?

OBJECTIVE: The objective of the study was to determine completeness of 24-hour urine collection in pregnancy. STUDY DESIGN: This was a retrospective laboratory/chart review of 24-hour urine collections at British Columbia Women's Hospital. Completeness was assessed by 24-hour urinary creatinine excretion ( UcreatV): expected according to maternal weight for single collections and between-measurement difference for serial collections. RESULTS: For 198 randomly selected pregnant women with a hypertensive disorder ( 63% preeclampsia), 24-hour urine collections were frequently inaccurate ( 13-54%) on the basis of UcreatV of 97-220 mu mol/kg per day ( 11.0-25.0 mg/kg per day) or 133-177 mu mol/kg per day ( 15.1-20.1 mg/kg per day) of prepregnancy weight ( respectively). Lean body weight resulted in more inaccurate collections ( 24-68%). The current weight was frequently unavailable ( 28%) and thus not used. For 161 women ( 81% proteinuric) with serial 24-hour urine levels, a median [ interquartile range] of 11 [ 5-31] days apart, between-measurement difference in UcreatV was 14.4% [ 6.0-24.9]; 40 women ( 24.8%) had values 25% or greater, exceeding analytic and biologic variation. CONCLUSION: Twenty-four hour urine collection is frequently inaccurate