Dietary Protein Ingestion (DPI) can be estimated from urinary urea excretion if a subject is in steady-state nitrogen balance, as nitrogen intake will equal nitrogen excretion. This information can be useful in patients on protein-restricted diets.
Testing: 24 hour urine analyzed for urea nitrogen in mg
dietary protein ingestion in grams per day =
= (((urinary urea nitrogen in mg per day) / (1440 minutes in day)) * 9.35) + 11
where:
• 9.35 is a factor derived from plotting a known protein ingestion in grams per day against the measured urea nitrogen excreted as milligrams per day
• 11 is the average, nonrenal nitrogen losses in grams per day of catabolized protein
dietary protein ingestion per kilogram body weight per day =
= (dietary protein ingestion in grams per day) / (body weight in kilograms)
Limitations:
• The assumption is that the patient is in steady state nitrogen balance, so that times of metabolic stress or starvation may result in inaccurate results.
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