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

Abstract

The objective of the study was to determine completeness of 24-hour urine collection in pregnancy. 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. 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 micromol/kg per day (11.0-25.0 mg/kg per day) or 133-177 micromol/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. Twenty-four hour urine collection is frequently inaccurate and not a precise measure of proteinuria or creatinine clearance.