Left side waist pain and blood in urine may be caused by upper urinary tract stones, acute pyelonephritis, kidney tumor and other reasons. 1. Upper urinary tract stones: such as the left side of the kidney stones, the patient may appear after the activity, the left side of the waist pain blood in the urine. If the left ureteral stone, there is often severe and intolerable pain in the left side of the waist, which can also radiate to the same side of the testicles or labia, and once the mucous membrane is damaged, the symptom of blood in urine can appear. 2. Acute pyelonephritis: acute bacterial inflammation of the renal pelvis and renal parenchyma, mostly from the urethra into the bladder, upward infection through the ureter to the kidneys, the left side of the lower back pain in the urine and blood symptoms. Patients are often accompanied by high fever, chills, urinary frequency, urinary urgency and other uncomfortable symptoms. 3. Kidney tumor: when the tumor grows and stretches the renal peritoneum or invades the lumbar muscle, invades the renal pelvis and renal calyces, the patient may have left-sided back pain and blood in urine, and there may be abdominal or lumbar lumps, etc. If the patient has left-sided back pain and blood in urine, the patient may have high fever, chills, frequent urination and other discomfort symptoms. If the patient has left-sided waist pain and blood in urine, it is recommended to consult a doctor in time, under the guidance of the doctor, improve the relevant examination, clarify the cause of the disease and target treatment.