The entire blood volume flows through the kidneys three hundred times a day: 1,500 liters of liquid, of which almost a tenth is initially filtered out. Only a small fraction of this gets out through the urinary tract together with waste materials as urine – the largest part is absorbed back into the bloodstream. In addition to blood purification, the kidneys have other important functions in our organism.
Symptoms of renal dysfunction
Disorders of kidney function are often only recognized during routine blood tests; in the case of diseases in the urinary system, on the other hand, complaints often lead the patient to the doctor. Typical symptoms that indicate diseases in the area of ​​the bladder and urethra are problems with urination such as increased urge to urinate , burning and pain when urinating, delayed urination, bladder weakness and changes in the smell or discoloration of the urine. They can indicate, for example, an irritable bladder, inflammation of the bladder or urethra, tumors or changes in the prostate.
However, other diseases can also manifest themselves as symptoms in the urinary tract, such as diabetes  due to increased urination (polyuria) or porphyria due to urine discoloration. Inflammation of the renal pelvis can manifest itself as aching pain in the flank and fever  , kidney or urinary stones cause massive colic if they get stuck.
The medical history
In most cases, by asking the patient specific questions about his or her medical history (anamnesis), the symptoms described can already be assigned to probable diseases. The focus is initially on the current symptoms – where, when and how often they occur, whether they started suddenly or have existed for a long time and whether there are other symptoms. Other past or chronic illnesses, previous surgeries or accidents, medications taken, and family illnesses are also important.
The basic diagnostics
The physical examination is usually performed with the patient standing and lying down. Externally visible signs of illness (inspection) are, for example, water retention and pale or yellowish skin.
During the palpation examination (palpation), the doctor can examine the kidneys (at least in slim people) and check the fill level and sensitivity of the bladder, especially if he uses his stethoscope to listen (auscultation) at the same time; When examining the rectum, the prostate can be felt. Tapping (percussion) in the area of ​​the flanks reveals pain in the kidney bearings – possible indication of inflammation or a stone.
One of the most important examinations for diseases in the area of ​​the urinary tract is the urine examination. Not only can the amount of urine be determined, but the urine sample can be examined under the microscope for admixtures (e.g. blood or inflammatory cells) and checked for the presence and amount of certain substances. Substances such as uric acid , proteins and sugar are usually not present or only in small amounts – and indicate metabolic diseases such as gout  and diabetes.
If an infection of the kidneys or bladder is suspected, a “urine culture” can be created with which germs can be determined. Blood samples are usually  examined at the same time, with which statements about kidney function can be made in particular.
