Urea is non-toxic, nitrogenous organic end product of protein metabolism enabling 80-90% of nitrogen elimination from human body. normally ,urea level in blood serum/plasma is in the concentration range of 3.3-6.7 mm, while its level > 30 mm concentration signify the requirement of dialysis in addition to other possible factors such as saline, water depletion, and gastrointestinal tract destruction.
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Metabolic wastes or excretes are substances left over from metabolic processes (such as cellular respiration) which cannot be used by the organism (they are surplus or toxic), and must therefore be excreted. This includes nitrogen compounds, water, CO2, phosphates, sulphates, etc. Animals treat these compounds as excretes. Plants have chemical "machinery" which transforms some of them (primarily the nitrogen compounds) into useful substances, and it has been shown by Brian J. Ford that abscised leaves also carry wastes away from the parent plant. In this way, Ford[citation needed] argues that the shed leaf acts as an excretory (an organ carrying away excretory products).
All the metabolic wastes are excreted in a form of water solutes through the excretory organs (nephridia, Malpighian tubules, kidneys), with the exception of CO2, which is excreted together with the water vapor throughout the lungs. The elimination of these compounds enables the chemical homeostasis of the organism.