Whether a single kidney is harmful mainly depends on whether the kidney function is normal or not. Kidney has strong compensatory function, for patients with normal kidney function, single kidney may not cause obvious harm; but for patients with renal insufficiency, single kidney may cause obstacles to the body’s metabolic waste discharge, regulation of water balance, metabolism and other functions are affected. 1. Metabolic waste discharge disorder: kidney can recycle glucose, amino acid, vitamins and other substances in the body filtrate, and discharge other metabolites such as creatinine, urea, uric acid, etc. to maintain the health of the body. Patients with single kidney renal insufficiency may cause the body metabolic waste elimination obstacles. 2. Regulate water balance: The kidney discharges excess water from the body through glomerular filtration and tubular reabsorption. Patients with renal insufficiency of a single kidney may suffer from edema, hypertension, or even cardiovascular and cerebrovascular accidents due to the obstacle of water excretion. 3. Metabolism: Kidneys can secrete renin, prostaglandin, erythropoietin and other hormones to take part in the regulation of vasodilatation inside and outside the kidney, in order to maintain the stability of the internal environment, so that metabolism can be carried out normally. Patients with renal insufficiency in a single kidney may affect the patient’s metabolic ability. If patients find that they have only one kidney, it is recommended that they go to a regular hospital to clarify their condition and standardize their treatment under the guidance of a doctor.