Testing the urine for kidney diseases:
General information:
A urine analysis may be necessary in the evaluation of kidney and urinary tract disorders. It can also be helpful in evaluating disorders of the whole body, such as diabetes or liver problems.
Collecting urine samples:
Usually, urine samples are taken from the morning urine because it is the most concentrated form of urine. Moreover, in general, the so called “midstream urine” (neither the first or the last part is collected) is used to lower the contamination risk with germs of the urethra or the patient’s skin, which could lead to a false test result. This technique is the so-called “clean-catch method”.
Urine is sterile. Consequently, if bacteria are found in the sample, an infection of the urinary tract is probably present.[2] Sometimes it is necessary to do a 24-hour urine collection for measuring various substances in the urine. The collection of urine over such a time period evens fluctuations which occur due to differing urine concentrations in the course of a day. The collection of the urine takes place under sterile conditions.[3]
Evaluation of the samples:
Macroscopic evaluation:
Freshly collected urine is normally always clear. The color can indicate the presence of a disease and, thus, be the start of further examinations for more precise clarification. Urine should be yellow-orange. Moreover, urine forms bubbles or is sometimes foamy. However, strong foam could be an indicator for proteinuria and, consequently, for a kidney disease. Furthermore, smell can be an indicator for some diseases.
It should be noted that discoloration and smell of the urine can also be caused by non-disease-related factors such as diet or the intake of pharmaceuticals. For example, beet turn urine red, large amounts of licorice turn it green and asparagus causes a characteristic stinky smell.
Microbiological examination:
If a urinary tract infection (UTI) is suspected, a microbiological examination of the bacteria found can be carried out. This allows the diagnosis to be confirmed and suitable treatment to be initiated. For this purpose, the bacteria are cultivated on suitable culture media and later examined more closely under the microscope by a specialist.
Urine test strip:
Right after urine collection, a plastic test strip can be dipped into the urine sample. On this strip are various reagent zones which are each assigned to a parameter and have a substance-specific indicator. After contact with the urine, they show a color change corresponding to the concentration of the substance detected. The test results can provide information on the status of carbohydrate metabolism, kidney and liver function, acid-base balance and the possible presence of an infection.
Testing for proteinuria:
The urine is not only examined for blood and cells, but also for protein. Protein excretion is an important marker for assessing kidney function. Normally, little to no protein should be detectable in the urine. Excessive excretion of protein in the urine (proteinuria) is an important indication of the possible presence of kidney disease. In some cases, very foamy urine indicates an increased protein content. The amount of protein in the urine can be determined by measuring the ratio of protein to creatinine in the urine. However, the amount of protein in the collected urine can also be examined. In this case, the urine is collected over a period of 12 to 24 hours and then sent to the laboratory.
Microscopic examination:
Additionally, the collected urine can be examined under the microscope. This allows a more precise evaluation of the urine which the bare eyes never could. A pathologist analyses and evaluates the sample and the cells contained. The amount as well as the type of the cells or found crystals can be an indicator for the presence of specific diseases.
Examples which may indicate a kidney disease:
The visible presence of blood in the urine. The urine is reddish in color.
The presence of a small amount of red blood cells (erythrocytes) in the urine. The color of the urine is normal. The erythrocytes are only visible on microscopic examination.
Abnormal protein excretion via the urine. The urine may start to foam (formation of visible bubbles).
Abnormally high urine production (more than 3 liters per day in adults). The urine appears colourless/clear.
Did you know?
Diabetes mellitus translates as “honey-sweet flow”. In the past, doctors diagnosed diabetes by tasting the urine of the patients, which tastes sweet due to the excretion of sugar via the urine. Fortunately, with the help of technical diagnostic tools, physicians no longer have to carry out this examination for the diagnosis.