What measurement is used to determine nitrogen balance?

• A. Blood urea nitrogen
• B. Urine creatinine
• C. Plasma amino acids
• D. Urine urea

Answer: (D)

Nitrogen balance is determined by comparing nitrogen intake with nitrogen losses, and the losses are largely through urine as urea, the main nitrogen-containing waste from protein breakdown. Measuring urinary urea excretion over a 24-hour period provides a practical and accurate estimate of daily nitrogen loss, which you then compare to nitrogen intake (from protein) to assess whether balance is positive, negative, or neutral. Blood urea nitrogen reflects a serum concentration rather than total daily excretion, urine creatinine is more about kidney function and urine collection validity, and plasma amino acids indicate amino-acid status rather than total nitrogen loss. So urinary urea is the measurement used to determine nitrogen balance.