Nutrition
Volume 21, Issue 3 , Pages 332-338, March 2005

Predicting total urinary nitrogen excretion from urinary urea nitrogen excretion in multiple-trauma patients receiving specialized nutritional support

Presented in part at the Third Annual Nutrition Week; Las Vegas, Nevada, USA; February 12, 2004.

  • Roland N. Dickerson, Pharm.D.

      Affiliations

    • Department of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee, USA
    • Corresponding Author InformationCorresponding author.
    • ,
  • Angelina C. Tidwell, Pharm.D.

      Affiliations

    • Department of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee, USA
    • ,
  • Gayle Minard, M.D.

      Affiliations

    • Department of Surgery, University of Tennessee Health Science Center, Memphis, Tennessee, USA
    • ,
  • Martin A. Croce, M.D.

      Affiliations

    • Department of Surgery, University of Tennessee Health Science Center, Memphis, Tennessee, USA
    • ,
  • Rex O. Brown, Pharm.D.

      Affiliations

    • Department of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee, USA

Received 30 March 2004; accepted 8 July 2004.

Abstract 

Objective

We investigated the accuracy of methods to estimate total urinary nitrogen (TUN) excretion from urinary urea nitrogen (UUN) excretion for patients who have multiple trauma and receive specialized nutritional support.

Methods

Fifty-five critically ill, adult patients who had multiple trauma and were receiving specialized nutritional support were evaluated. A 24-h urine collection for urea nitrogen and total nitrogen was performed 4.4 ± 2.6 d after admission to the trauma intensive care unit. Patients with significant renal impairment, liver dysfunction, or obesity (>150% of ideal body weight) were excluded from study entry. Eight publications that examined the relation between TUN and UUN were evaluated for bias and precision in estimating TUN from UUN.

Results

TUN was 20.8 ± 10.8 g/d with an average difference of 3.8 ± 2.8 g/d between TUN and UUN. Linear regression analysis comparing TUN with UUN indicated a significant correlative relation (TUN = 1.1 × UUN + 2; r = 0.958, P < 0.001). The difference between TUN and UUN varied based on UUN: for UUN lower than 10 g/d, TUN minus UUN was 1.5 ± 1.0 g/d; for UUN 10 to 20 g/d, TUN minus UUN was 4.1 ± 3.2 g/d; and for UUN higher than 20 g/d, TUN minus UUN was 5.3 ± 1.9 g/d (P < 0.001). Six methods were biased toward underpredicting TUN, one method was unbiased, and one was biased toward overpredicting TUN. A practical method for estimating TUN from UUN was developed: TUN = UUN + 2 for those with UUN lower than 10 g/d and TUN = 1.1 × UUN + 2 for those with UUN of at least 10 g/d.

Conclusions

Our method, the modified Velasco method, UUN/0.84, and UUN/0.85 provided reasonable estimates of TUN from UUN in critically ill, adult patients who had multiple trauma and were receiving specialized nutritional support; however, our method requires further validation.

Keywords:  Nitrogen balance , Protein requirements , Catabolism , Parenteral nutrition , Enteral nutrition , Nutritional assessment

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 This study was supported in part by the American Society for Parenteral and Enteral Nutrition, Rhoads Research Foundation, and B. Braun Medical, Inc.

PII: S0899-9007(04)00294-1

doi:10.1016/j.nut.2004.07.005

Nutrition
Volume 21, Issue 3 , Pages 332-338, March 2005

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