Why the urine is so important (aka Urinalysis)… (Day 122)

Urine Sample for Urinalysis

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One of the cheapest, quickest and most basic of tests used within veterinary practice is that of urinalysis, where the urine is examined and used to help diagnose disease. This test can be used as an indicator of disease in the kidneys, with digestion and within the urinary tract itself.

The first step in urinalysis is actually collecting the urine to examine, now unlike humans animals tend to have a problem with peeing in a cup. Now for certain parts of urinalysis such as culture in a microbiology laboratory a sterile sample is essential, and this is normally collected using cystocentesis which is where a needle is inserted directly into the bladder. For general tests however less invasive methods are used to collect the urine as it flows (takes practice) or with cats using a non-absorbing litter in their tray for example. If this fails when an animal is proving difficult to collect a sample from a catheter can be used instead and is passed along the urinary tract and into the bladder. It is important that urine is examined as soon as possible because it deteriorates with artifacts such as the pH changing and the formation of crystals.

Urine Sample for Urinalysis
Urine Sample

Now once a sample is collected the first thing to do is to examine the gross sample for the appearance and smell of the urine. Previously in history doctors actually even tasted the urine however luckily that is not done anymore (on purpose anyways!)! The colour of the urine should be slightly transparent and yellow or amber, it should not be cloudy and the odour should be faintly that of ammonia.

Next the urine’s specific gravity is tested, this can either be done with a refractometer or with a hydrometer (which is something new I learnt here). This tells us the concentration (the liquid:solid ratio) of the urine which is how many water soluble molecules (such as toxins, waste products, metabolic waste) there are in the urine. The reference (normal) values for the specific gravity depend on the species of the animal being tested. Though not a complete list some of the diseases that this points to include dehydration, renal failure, excessive drinking, diabetes insipidus, glycosuria, decreased kidney blood flow and many more.

A dipstick test is then carried out to check many different parameters at once, depending on the test stick used this can include pH, glucose, leukocytes, blood (hemoglobin) content, Nitrates, Ketones, Bilirubin and Protein. Some sticks contain specific gravity however its not as reliable as using one of the previous test methods. Something worth remembering here is that once urine is applied the stick should kept horizontal to prevent contamination between the tests. In fact some places actually pipette a drop of urine onto each test square instead of dipping the stick! All of these parameters point to different diseases and body systems.

Finally the urine is examined under the microscope for cells, crystals, parasite eggs, and fat all of which should not be present in urine. Cells can indicate problems physically with the tract and bladder, whilst crystals can indicate further problems with bladder stones. Parasite eggs obviously indicate parasites, whilst fat is an indicator for digestion and renal diseases.

This is just one piece of the diagnosis puzzle that a vet works with, and because of the relatively low cost of urinalysis and ability to perform the test instantly in house is one of the most valuable.