The kidneys are responsible for numerous physiological functions. They filter your blood from toxic substances, regulate your blood pressure, and even produce a hormone which controls the production of red blood cells (erythrocytes). Kidney failure can have different causes, such as cardiovascular disease, bacterial and viral infections, autoimmune diseases, etc. However, the first symptoms are usually similar in all those cases. If you notice any of the following symptoms, you are advised to visit your doctor and perform some routine tests of kidney function.