Renal function urea is a test that examines blood and is used clinically to re-evaluate renal function based on the adequacy of excretion of certain toxins. The substances selected require filtration through the kidneys and little reabsorption through the kidneys. Those that can meet this criterion are urea, and creatinine. Checking urea is mainly a blood test. Urea is a product of protein metabolism, so its high or low level is easily influenced by protein. If you are on a high protein diet during the days of kidney function check, it may lead to the increase of urea. Therefore, it is important to have a light diet before this test. In addition, the level of urea is also easily affected by blood pressure. If the patient has diarrhea, vomiting, or sweating more in the recent period, it will lead to low blood pressure, which will easily cause insufficient kidney perfusion and elevated urea. Therefore, it is important to maintain a stable blood pressure before checking this.