Urine is the body’s way of getting rid of excess substances such as metabolic waste products, medications and toxins. Urine is also part of a regulatory mechanism that keeps fluid and electrolytes in balance. Its analysis can provide clues to various disorders.
Composition of urine
Urine is 95% water, in addition to containing metabolic (end) products such as urea, uric acid, and creatinine, salts, acids, dyes, hormones, and water-soluble vitamins. Urine is formed in the two kidneys, collected in the associated renal pelvis and passes through the two ureters into the urinary bladder. The urge to urinate arises as soon as a certain filling state is reached there; urination via the urethra can be controlled voluntarily.
In healthy individuals, the consistency of the urine and the frequency of bladder emptying depend on the amount of fluid absorbed and lost through the skin and respiration. Per day, the kidneys initially produce about 150 liters of urine and ultimately reduce this amount to 1.5-2 liters, which are excreted.
The typical urine odor is caused by uric acid and ammonia. The latter is formed more frequently when urine stands for a longer period of time and is responsible for the pungent odor. The urine gets its color from bile pigments, which are formed during the breakdown of red blood cells. It varies from light to dark yellow depending on the degree of dilution.
Changes in urine: causes
One or more of the factors described above may be altered by pathological processes such as cystitis and kidney disease, thus aiding in diagnosis. In addition, blood, cells, pathogens, and other admixtures can be searched for. In the case of certain metabolic disorders, enzymes and hormones can be measured, and special tests can follow in the case of disorders of kidney or bladder function.
The following are typical causes of changes in urine color, volume and odor:
- Color: Certain foods such as blackberries (reddish brown) and rhubarb (lemon yellow) or medications such as antibiotics (brown) and vitamin tablets (orange) cause temporary discoloration. In cases of disease or injury to the kidneys or urinary tract, protein, red and white blood cells, or bacteria can cause turbidity or red discoloration. Liver inflammation and transfusion incidents or porphyria can also cause red discoloration of urine. Alkaptonuria, a rare metabolic disease colors the urine brown-black, and in the case of liver inflammation, it can also become dark brown to greenish and show yellow foam when shaken.
- Quantity and odor: in disorders of kidney function, urine production may be limited, in certain metabolic diseases such as diabetes or medication, there is increased urine production and very light urine. Changes in odor can be caused by food – for example, after eating asparagus, a typical odor occurs in about half of people. Strong-smelling urine is a result of a bacterial infection, and a foul odor may be caused by bladder tumors. A sour, acetone-like odor is typical in diabetes if it is not well controlled.
Obtaining a urine sample
In general, the sample is obtained from the midstream urine, that is, the middle portion of urine of about 20-40 ml, which is collected – without interrupting the urine stream – after the first portion is emptied into the toilet. This is to ensure that any germs contained do not originate from the external genitalia but from the urinary tract. To reduce the risk of sample contamination and thus ensure the validity of the analysis, the individual should observe the following points:
- The urine must be collected in a sealable, clean urine cup. Physician or pharmacist provide this.
- The genitals must be washed thoroughly beforehand.
- When urinating, the woman should spread her labia, the man should pull back his foreskin.
In special cases, if the urine must be safely sterile, it can also be obtained by the doctor through a catheter or direct puncture of the urinary bladder through the abdominal wall.
