Protein Intake: 95g 24hr Urinary Urea Nitrogen = 15g Calculate the Nitrogen balance formula – Nitrogen Balance = Nitrogen intake – Nitrogen losses Nitrogen intake = Protein intake (g/day) / 6.25 Nitrogen losses = Urinary Urea Nitrogen (g/day) + 4g
The Correct Answer and Explanation is:
Nitrogen Balance Calculation
Given:
- Protein intake = 95 g/day
- 24-hr Urinary Urea Nitrogen (UUN) = 15 g/day
- Nitrogen intake = Protein intake / 6.25
- Nitrogen losses = UUN + 4 g (miscellaneous losses)
Step 1: Calculate Nitrogen Intake
Nitrogen intake = 95 g / 6.25 = 15.2 g/day
Step 2: Calculate Nitrogen Losses
Nitrogen losses = 15 g (UUN) + 4 g = 19 g/day
Step 3: Calculate Nitrogen Balance
Nitrogen balance = Nitrogen intake − Nitrogen losses
Nitrogen balance = 15.2 g − 19 g = −3.8 g/day
Interpretation and Explanation
Nitrogen balance is a clinical tool used to assess whether the body is in a state of anabolic (building) or catabolic (breaking down) metabolism. It compares nitrogen intake (mostly from dietary protein) to nitrogen losses (primarily through urine as urea, with an additional estimate for other losses like sweat, feces, and skin).
In this example, a protein intake of 95 g/day yields a nitrogen intake of 15.2 g/day (since protein is approximately 16% nitrogen, dividing by 6.25 gives nitrogen content). Urinary urea nitrogen (UUN) measures the nitrogen excreted in the urine and is reported here as 15 g/day. Because not all nitrogen is lost through urine, an estimated 4 g/day is added to account for miscellaneous routes of loss.
The calculated nitrogen balance is −3.8 g/day. This negative nitrogen balance indicates that nitrogen losses exceed intake. It suggests the individual is in a catabolic state, where the body is breaking down muscle or other protein-rich tissues. This is commonly seen in cases of severe illness, trauma, malnutrition, or inadequate protein intake. Persistent negative nitrogen balance can lead to muscle wasting, impaired immune function, and delayed wound healing.
Conversely, a positive nitrogen balance (intake > losses) would indicate tissue growth or repair, as seen in children, pregnant women, or individuals recovering from illness or injury.
Monitoring nitrogen balance helps guide nutritional interventions in hospitalized patients or those with critical illness to ensure adequate protein intake for recovery and maintenance of lean body mass.
