Corpus: Urine

Urine is an excretory product produced in the kidneys by a complex filtration and reabsorption process (diuresis). It is channelled via the two ureters to the urinary bladder, where it is collected and released via the urethra during micturition.

Metabolic end products such as urea and uric acid are disposed of via the urine and excess body fluid (water) is excreted.

The main components of urine are water, urea and electrolytes. Other components of urine are

• creatinine
• Uric acid
• Organic acids (e.g. citric acid)
• Water-soluble vitamins
• Hormones
• Colouring agents (urochromes)

Proteins are also present in small quantities. The exact composition of urine is regulated by complex transport processes in the renal tubules.

Contrary to older textbook opinion, the urine collected in the bladder is not completely germ-free in healthy people. Routine clinical measures cannot detect germs in catheter urine and bladder puncture urine in women. However, PCR and special cultivation measures show that human urine in the bladder has its own microbiome, which consists mainly of bacteria of the genera Aerococcus and Actinobaculum, as well as smaller proportions of Escherichia and Shigella.^[1]

After micturition, the urine is additionally contaminated by germs in the urethra, so that it contains up to 10,000 germs per millilitre on discharge.

The normal aspect of urine is clear and slightly yellowish to amber in colour. The intensity of the urine colour depends on the concentration of urochromes. Hypertonic urine is intensely yellow, hypotonic urine can be water clear. Fresh urine is normally almost odourless; it only acquires a pungent ammoniacal odour through subsequent bacterial decomposition. A deviating, unusual urine odour can be an indication of certain metabolic diseases (e.g. diabetes mellitus).

Colouration[Bearbeiten]

The colour of urine is influenced and changed by dietary habits, fluid intake, metabolic changes, illnesses and, last but not least, the intake of medication.^[2] If it is suspected that a drug or its metabolites have caused the discolouration, information should be obtained from a poison information centre.

One example is the purple discolouration of urine in purple urine bag syndrome (PUBS).^[3]

The daily urine volume is about 1 to 1.5 litres. Deviations from this reference range are characterised by the following terms

• Polyuria: increased urine production
• Oliguria: reduced urine production
• Anuria: stopped urine production

...according to micturition phase[Bearbeiten]

• First stream urine
• Midstream urine
• Final stream urine

...according to micturition time[Bearbeiten]

• Morning urine

...by collection method[Bearbeiten]

• Catheter urine
  • Disposable catheter urine
  • Urine from urinary catheter
• Bladder puncture urine (BPU)
• 24-hour urine collection

see also: Urine sample

The analysis of urine and its components (urine diagnostics) is a routine laboratory diagnostic test. As a rule, midstream urine is used for this purpose. The summarised results of the tests are referred to as urine status.

If the pH value of the urine is reduced due to an increased acid content, this is referred to as aciduria. The opposite, i.e. an increased pH value, is alkaliuria.

In the context of infectious diseases, microorganisms can pass into the urine. Depending on the type of pathogen, this is referred to as:

• bacteriuria
• viruria
• parasituria