The Estimation of 24‐Hour Urine Urea Nitrogen Excretion from Urine Collections of Shorter Duration in Continuously Alimented Patients

Urine urea nitrogen excreted in 24 hr is used to estimate nitrogen balance in patients. Normal diurnal variation of urea excretion may be less pronounced in patients alimented continuously, and a urine collection of shorter duration may be representative of the 24-hr excretion. Five stabilized trauma center patients on continuous enteral or parenteral alimentation were studied with six consecutive 4-hr urine collections analyzed for urine urea nitrogen content. Excretion rates for various lengths of urine collection were compared with the 24-hr excretion rate. Urine collections spanning 4 or 8 hr frequently exceeded an error of 10% in predicting 24-hr urea nitrogen excretion, while collections of 12 hr or more had small errors. A comparison of three consecutive 8-hr collections was suggestive of diurnal variation existing under these conditions.