Damage to the kidney by an external force, of necessity quite considerable if the kidney is healthy, because the organ is well protected in the body. Diseased kidneys are more susceptible to injury. The commonest and least serious injury is a contusion, causing tiny breaks in the kidney tissue which bleed slightly and cause swelling. If the injuries are more serious they can cause total or partial tearing of kidney tissue, and the renal pelvis and capsule can also be damaged, with consequential severe haemorrhage in and around the kidney. The most serious injury of all is crushing of the kidney or tearing of the large blood vessels, leading more rapidly to severe haemorrhage. There is a high risk of shock because other organs are often damaged as well. Symptoms of renal injury are blood in the urine (haematu- ria), pain in the side and upper abdomen, nausea and vomiting. Diagnosis is confirmed by the presence of blood in the urine (possibly visible only under the microscope), X-rays of the abdomen, and contrast X-rays of the kidneys and renal blood vessels. Slight renal injuries are treated with bed rest, to reduce haematuria; more severe injuries require surgery to repair as much of the damage as possible. Often time is allowed to elapse so that the haemorrhage has a chance to subside. With crushing of the kidney or tearing of blood vessels, immediate surgery is necessary. Sometimes the kidney has to be wholly or partly removed; if the other kidney is intact, this causes no problems.