Why does BUN Level Increase?

Why does BUN level increase? BUN is short for blood urea nitrogen, which is a final metabolism of protein. It discharges out of the body through kidney. The normal range of adult BUN is 3.2～7.2 mmol/L(9～20mg/dl). If the examination result is higher than 7.2mmol/L, we consider it is high and long time high blood urea nitrogen will damage the body for it is metabolism waste after all which should have been discharged out of the body. So if the level of blood urea nitrogen is high, it in most of time indicates that there is damage in the kidney. On the other hand, it may also be connected with the excessive intake of protein. Next, we will have a detailed explanation.
1. Too much intake of protein can lead to the high blood urea nitrogen. In the metabolism of protein, NH3 and C02 are produced, which combine into urea in liver. Generally, 1g protein can metabolize 0.3 urea. In addition, the ratio of nitrogen in urea and urea is 28/60. We can also say that the amount of nitrogen is nearly 50%. However, we do not need to be worried for the increased level is temporary and after rest of decreased intake of protein, the level of BUN (blood urea nitrogen) will turn normal.
2. The discharging ability of kidney decreases, which leads to the increase level of BUN(blood urea nitrogen). Kidney is an important organ which discharges urea. After being filtrated in renal glomeruli, urea can be reabsorped in renal tubules. After urea reaches renal tubules, the more the speed the urinating is, the more urea will be discharged out of the body. From the above, we can find out that renal glomeruli and renal tubules are the main renal tissue which influence the discharging of urea.
In renal glomeruli, there is basilar membrane which has pores. Through the pore, small molecules can be discharged. However, when kidney is damaged, the pores will be damaged and urea can not discharge well, thus causing high level of blood urea nitrogen in the blood.