High urea nitrogen is actually the clinical significance of increased urea nitrogen, including the following aspects: first, increased blood urea nitrogen in organic renal impairment, such as chronic renal failure due to various primary glomerulonephritis, pyelonephritis, interstitial nephritis, etc. Blood urea nitrogen cannot be used as an indicator of early renal impairment, but in chronic renal failure, especially in uremic patients, the degree of increased blood urea nitrogen is usually consistent with the disease Secondly, increased blood urea nitrogen is also seen in pre-renal and post-renal factors, the former including severe dehydration, massive ascites, cardiac circulatory failure, etc., and the latter such as urinary tract obstruction caused by ureteral stones and other diseases; thirdly, blood urea nitrogen can be used as an indicator of dialysis adequacy in renal failure.