Kidney and urinary tract tests: Tests of kidney function and bladder function

There are a number of methods that can be used to check the kidneys’ excretion capacity and ability to concentrate, kidney blood flow and the functionality of the urinary bladder:

functional tests

• Urea  and  creatinine : The concentration of urea and creatinine in the blood gives a rough overview. These substances are filtered and excreted from the blood by the healthy kidneys. If kidney function is impaired, its concentration in the blood therefore increases. A more precise picture is given by the  creatinine clearance , in which the concentration of creatinine in the blood and in the urine collected over 24 hours is determined and related to one another.
• PAH clearance : p-aminohippuric acid is injected into the patient’s vein and its concentration in blood and urine is determined. This allows conclusions to be drawn about the renal blood flow.
• Inulin clearance : Inulin is injected instead of PAH; the test allows a statement to be made about the filtration performance in the kidney corpuscles.
• Volhard test : The patient stops drinking water and the urine concentration is measured at regular intervals. This increases continuously in healthy people.
• Kidney scintigraphy (radionuclide nephrography) : The patient is injected with a radioactive substance that is stored in the kidneys or excreted in the urine. The extent of enrichment over several phases can be recorded with a special camera. In this way, blood circulation, filter function and urination can be assessed and different diseases can be distinguished from one another. In addition, it is an important examination after a kidney transplant in order to detect rejection reactions at an early stage.
• Urodynamics : This generic term includes various examinations with which the function of the urinary bladder and its sphincters can be checked: determining the amount of urine that flows through the urinary bladder within a certain period of time, the pressure in the bladder and checking using ultrasound whether there is any urine after the voiding still urine.