Reversible azotemia is a condition in which there is a significant increase in blood levels of non-protein nitrogen (NPN), such as urea, creatinine, and uric acid, called azotemia. In normal individuals, NPN in the blood is 25-35 mg%, with urea nitrogen at 10-15 mg%. Azotemia is a biochemical term that has both a broad and a narrow concept. The broad concept is that as long as the blood urea nitrogen or creatinine and other non-protein nitrogen exceeds the normal range, it can be called azotemia. A variety of kidney diseases that do not heal, late renal impairment can occur, so that the nitrogen excretion in the blood is impaired, so the accumulation in the blood, which is the result of renal failure. However, if a normal person eats a lot of high-protein food in a short period of time, such as over the New Year holidays or usually attending too many parties, although the kidney function is normal, but cannot excrete too much nitrogen rapidly in a short period of time, then a transient azotemia will occur. The narrow concept is that when the chronic renal insufficiency stage of kidney disease patients, the urea nitrogen and creatinine in the blood are above the normal range, this period is called the azotemia period, or pre-uremia. Its occurrence is mainly due to renal excretion dysfunction and increased protein breakdown in the body (e.g. infection, poisoning, severe tissue trauma, etc.). During this period, azotemia progressively worsens and uremia can develop in severe cases. The normal value of blood urea nitrogen contained in general test books is ≤7.1 mmol/l (20 mg%) and the normal value of blood creatinine is ≤176.8 micromol/l (2 mg%). In fact, blood urea nitrogen should be ≤5.3 mmol/l (15 mg%) and blood creatinine should be ≤132.6 micromol/l (1.5 mg%) in the period of normal renal function. And blood urea nitrogen 5.7-7.1 mmol/l (16-20 mg%), blood creatinine 141.4-176.8 micromol/l (1.6-2 mg%) stage of renal function has been abnormal, but can compensate without azotemia, so it should be called the compensatory stage of renal insufficiency.