urea nitrogen appearance, the amount of urea in grams produced by a person’s body over a specific period of time, closely related to the amount of nitrogen that has not been absorbed by the body. It is calculated as the sum of the urea excreted in the urine plus that found in the blood by calculating blood urea nitrogen. A low figure indicates efficient use of dietary protein. The person’s intake of protein must also be known because a low urea nitrogen appearance is also seen with a low protein diet or malnutrition.
