What is the primary waste product from protein metabolism found in urine?

Urea is the primary waste product from protein metabolism found in urine because it plays a key role in removing excess nitrogen from the body. When proteins are metabolized, amino acids are deaminated, resulting in the production of ammonia, which is toxic in high concentrations. The liver quickly converts ammonia into urea through the urea cycle, making it less toxic and more water-soluble. This urea is then transported to the kidneys for excretion in urine.

While uric acid, creatinine, and ammonia are also related to nitrogen metabolism, they are not the primary waste product involved in the excretion of excess nitrogen from protein metabolism. Uric acid is mainly a product of purine metabolism, creatinine is a byproduct of muscle metabolism, and ammonia, although initially produced from amino acid deamination, is converted to urea for safer excretion. Thus, urea's central role in nitrogen elimination makes it the primary waste product associated with protein metabolism in urine.