Nitrogen, Total, 48, 72, or 96 Hours, Feces
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Nitrogen is a key component of proteins. During protein catabolism (proteolysis), nitrogen is excreted in the urine and feces. Protein catabolism may be increased after stress (eg, physical trauma, surgery, infections, burns).
"Nitrogen balance" is the difference between the amount of nitrogen ingested and the amount excreted. A patient who is in negative nitrogen balance is using muscle protein to meet the metabolic requirements of the body and is, therefore, in a catabolic state.
Assessing nutritional status (protein malnutrition), evaluating protein catabolism, and determining nitrogen balance, when used in conjunction with 24-hour fecal nitrogen measurement.
Average fecal nitrogen excretion is approximately 2 g/day, but fecal nitrogen excretion is highly variable, especially in conditions resulting in excessive protein catabolism. Significantly abnormal excretion rates, resulting in negative nitrogen balance, may be associated with severe stress due to multiple trauma, head injury, sepsis, or extensive burns. Elevated values >2.5 g total fecal nitrogen/24 hours are usually found in cases of chronic progressive pancreatitis. The goal with therapy for a depleted person is a positive nitrogen balance of 4 g to 6 g nitrogen/24-hours.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Send ENTIRE STOOL COLLECTION (must contain at least 10 g of feces) frozen on dry ice in Mayo Medical Laboratories approved container.
Measurement of both urine and fecal nitrogen is necessary for the accurate determination of nitrogen balance.
Specify length of collection period and total weight of entire stool specimen.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
<16 years: not established
> or =16 years: 1-2 g/24 hours
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Phinney SD: The assessment of protein nutrition in the hospitalized patient. Clin in Lab Med 1981;1:767-774
2. Veldee MS: Nutritional assessment, therapy, and monitoring. In Tietz Textbook of Clinical Chemistry. Third edition. Edited by CA Burtis, ER Ashwood: Philadelphia, WB Sanders Company, 1999; pp 1385-1386
3. Konstantinides FN, Kostantinides NN, Li JC, et al: Urinary urea nitrogen: too insensitive for calculating nitrogen balance studies in surgical clinical nutrition. J Parenter Enteral Nutr 1991;15:189-193