Nonrenal causes of increased levels of urea might include:

• A. The amount of carbohydrate ingested
• B. The amount of protein ingested
• C. Insufficient insulin
• D. Insufficient ADH

Answer: (B)

Nonrenal increases in urea come from more nitrogen being processed by the liver into urea, not from the kidneys. When more protein is consumed, there are more amino acids to deaminate, and the liver converts the resulting ammonia into urea. This directly raises the amount of urea produced and circulating, even if the kidneys are functioning normally, so dietary protein intake is the clearest nonrenal driver of higher urea levels.

Carbohydrates don’t feed into the urea cycle the same way; they mainly supply energy and can even spare protein from breakdown, so they’re not a direct source of increased urea. Insufficient insulin can cause more protein breakdown and could raise urea indirectly, but that’s not a direct dietary factor like protein intake. Insufficient ADH affects water balance rather than urea production.