Focal nephrogenesis is caused by acute renal failure. Acute renal failure is a clinical syndrome in which the urinary function of the kidney is drastically reduced by the kidney itself or by extra-renal causes, resulting in serious disturbances in the internal environment of the body. The clinical differential diagnosis is as follows: 1. Differentiation from pre-renal azotemia (1) Rehydration test: Those who have a history of volume deficiency and fluid loss before the onset of the disease, and whose physical examination reveals dry skin and mucous membranes, hypotension, and inconspicuous jugular venous filling, should first consider pre-renal oliguria, and may try infusion (200-250 ml of 5% glucose solution) and injection of collaterals diuretics (40-100 mg of furosemide). to observe the circulatory system load after infusion. If blood pressure returns to normal and urine output increases after replenishment of blood volume, the diagnosis of prenephrotic oliguria is supported. Those with prolonged hypotension, especially in the elderly with poor cardiac function, and no increase in urine volume after rehydration should suspect that prerenal azotemia has transitioned to ATN. (2) Urine diagnostic index examination. (2) Differentiation from post-renal urinary tract obstruction History of primary disease leading to urinary tract obstruction such as stone, tumor, prostatic hypertrophy; sudden decrease in urine volume or alternating with anuria; patient’s self-conscious renal colic, pain in the hypochondrium or lower abdomen; percussion pain in the renal area; if obstruction at the bladder outlet, the bladder area is swollen due to urine accumulation and a turbid sound on percussion; no significant change in urine routine. Ultrasonography and X-ray can help confirm the diagnosis. 3. Identification of glomerular or renal microvascular disease Severe acute glomerulonephritis, acute nephritis, secondary nephropathy such as lupus nephritis, purpura nephritis and nephrotic syndrome with massive proteinuria can also cause idiopathic acute kidney injury. In addition, some of them are caused by small vessel vasculitis, hemolytic uremic syndrome and malignant hypertension. According to the medical history, laboratory tests and kidney biopsy can help to identify. 4. Differentiate from acute interstitial nephritis based on the history of recent drug use, clinical manifestations such as fever, rash, lymph node enlargement and joint pain, blood eosinophilia, and abnormal urinalysis with renal tubular and glomerular function injury. Kidney biopsy can help to confirm the diagnosis. 5. Differentiate from renal vascular obstruction Bilateral renal or isolated renal artery embolism or venous thrombosis can cause acute kidney injury, which is rare clinically and can manifest as severe back pain, hematuria and anuria. Angiography can make a clear diagnosis.