What marker is used primarily to monitor protein intake during nutrition support?

• A. Serum albumin
• B. Urine urea nitrogen
• C. C-reactive protein
• D. Total nitrogen excretion

Answer: (B)

The key idea is that protein adequacy in nutrition support is best judged by tracking nitrogen losses, because the nitrogen you provide with protein should roughly balance what you lose. Urine urea nitrogen is the practical marker used for this purpose because most daily nitrogen losses occur in urine as urea, and measuring UUN gives a timely read on the body’s protein metabolism and intake. Serum albumin and C-reactive protein reflect other processes—albumin changes with inflammation, hydration, and liver function and responds slowly; CRP indicates inflammatory status, not how much protein you’re supplying. Total nitrogen excretion would include all losses (urine, stool, skin, wounds), which is difficult to measure routinely; UUN provides a straightforward, accessible proxy for the nitrogen that needs to be balanced with intake. In practice, you compare nitrogen intake (protein grams divided by 6.25) to nitrogen losses estimated by UUN (plus a small allowance for non-urinary losses) to guide adjustments in protein provision and reach a balanced plan.