The increase of BUN suggests that the urea nitrogen is higher than normal, which is most commonly seen in acute renal insufficiency or chronic renal insufficiency clinically, and it is recommended to go to hospital to further identify the cause. In case of acute renal insufficiency, both urea nitrogen and creatinine can be elevated, which is usually seen in acute deficiency of blood volume such as massive nausea and vomiting, or recent application of nephrotoxic drugs, resulting in acute kidney damage, or acute urinary tract obstruction resulting in inability to discharge urine and obstructive nephropathy. If it is chronic renal insufficiency, elevated urea nitrogen and creatinine consider whether it is combined with chronic glomerulonephritis, hypertensive renal damage, diabetic nephropathy, vasculitis renal damage and other diseases, determine the primary cause according to the medical history, clinical manifestations and auxiliary examination, and actively carry out renal preservation treatment.