The kidneys can be damaged by inflammation or toxic substances. When this occurs, harmful substances will start to accumulate in the blood. The blood can be cleaned in a process known as dialysis, which has to be repeated a couple of times a week. The patient's blood needs to flow through the dialyzer for several hours in order for the blood to become adequately clean and for excess fluid to be removed from the body. Another possibility is to transfer a kidney to the patient, for example from a relative.

An urine sample can be used to detect diseases or foreign substances in the body. If a person has excess sugar in their urine, it is often a sign of diabetes. Diabetes occurs when healthy blood sugar levels are not maintained. In diabetes, a person has so much glucose in their blood that the kidneys cannot return all of it back to the bloodstream. Diabetes is usually caused by a lack of insulin in the pancreas.

Blood cells or proteins in the urine may be a symptom of kidney inflammation. Bacteria in the urine, in turn, refer to urinary tract infection, which is a common and painful illness.

Doping substances that may have been used to improve competitive performance are often detected in urine tests.