There are a number of procedures that can be used to check the excretory capacity and concentrating ability of the kidneys, renal blood flow, and urinary bladder function:
Functional tests
- Urea and creatinine: A rough overview is given by the concentration of urea and creatinine in the blood. These substances are filtered from the blood and excreted by healthy kidneys. If kidney function is impaired, their concentration in the blood therefore increases. A more accurate picture is given by the creatinine clerance, in which the concentration of creatinine in the blood and in urine collected over 24 hours is determined and correlated.
- PAH clearance: the patient is injected with p-aminohippuric acid into the vein and its concentration in blood and urine is determined. This allows conclusions to be drawn about renal blood flow.
- Inulin clearance: inulin is injected instead of PAH; the test allows conclusions to be drawn about filtration efficiency in the renal corpuscles.
- Volhard test: the patient stops water intake and urine concentration is measured at regular intervals. This increases continuously in the healthy person.
- Renal scintigraphy (radionuclide nephrography): the patient is injected with a radioactively labeled substance, which is stored in the kidneys or excreted in the urine. The extent of accumulation over several phases can be recorded with a special camera. This makes it possible to assess blood flow, filter function and urinary output and thus to distinguish between different diseases. In addition, it is an important examination after a kidney transplant to detect rejection reactions at an early stage.
- Urodynamics: this generic term includes various examinations that can be used to test the function of the urinary bladder and its sphincters: Determining the amount of urine that passes through the bladder within a certain period of time, the pressure in the bladder and testing by ultrasound whether there is still urine in it after emptying.
