A typical urinalysis includes determining the Specific Gravity (SG), verifying the urine's chemical properties and an examination for sediments under the microscope. The instruments we require are minimal, readily available and affordable, so there should really be no excuses.
In this article we’ve decided to look at some of its applications and advantages to try to encourage us all to use it more.
Collecting a urine sample
Before we can analyse our sample, we need to collect a representative amount of urine in a safe and reliable way. There are a number of methods we can use, and these can be achieved with the help of the owner or by ourselves in the clinic.
- Midstream free-catch samples – these are useful when collecting urine to measure SG and glucose, but contact with the distal urinary tract, fur and a non-sterile receptacle make these samples less useful when looking to culture. Home samples are often collected this way by owners and there is absolutely no risk to the patient.
- Litter tray samples – urine collected in a clean litter tray with non-absorbent litter is helpful when attempting to monitor the morning glucose levels.
- Cystocentesis – this is the ideal method to collect urine if you need a sample for culture. It’s generally a safe procedure, especially if the patient is cooperative and the bladder can be identified and stabilised, though injury and adverse reactions can occur such as lacerating the bladder and colon.
- Catheterise – this method is frequently used when animals are hospitalised and can be helpful in monitoring patients over several days. There is the potential for trauma, haematuria and the introduction of bacteria into the bladder from the urethra.
- Manual expression – this caries the risk of trauma to the bladder with haematuria if carried out too forcefully. The sample can also be contaminated with cells, bacteria and other debris located in the genital tract, or on the skin and hair.
The physical urinalysis examination
A typical urinalysis will start with the gross examination of the sample. Simple observations can offer some important information, so begin by looking at and recording the following;
This is always considered in association with the SG and volume.
- Colourless - transparent urine may indicate over-hydration.
- Pale straw colour – this would be considered normal in a healthy, well-hydrated animal.
- Transparent yellow - this again is normal.
- Dark yellow – this is most likely normal but may suggest mild dehydration.
- Amber colour – this might indicate slight dehydration.
- Light orange – the animal might be dehydrated, but this may also be caused by liver or bile duct problems or the excretion of an excess of B vitamins.
- Dark orange or brown – this might be a symptom of jaundice or rhabdomyolysis. It can also be caused by severe dehydration.
- Pink or red – this may be as a result of blood (haematuria). In rabbits it can be completely normal from pigments in the food. It can also be benign, idiopathic or a sign of a renal stone. Red urine should always be investigated.
- Dark brown or black - some medications can significantly darken urine, such as high doses of metronidazole.
- White or milky urine – this can be caused by minerals, such as calcium or phosphate, a urinary tract infection or excessive proteins.
Freshly voided urine from the healthy animals is usually clear, except in rabbits, when it might be cloudy due to the presence of calcium carbonate. Cloudy urine may not necessarily indicate abnormal pathology, as many samples become cloudy upon standing.
Foul smelling urine is often an indicator of infection. Concentrated urine will also have a stronger smell.
D. Urine Dipsticks
- These are our standard ‘go to’ tool in the consulting room when checking urine. They are extremely useful, but also have some problems we need to be aware of. Most of them are designed for human use, so have limitations.
- Some dipsticks show areas for testing for urobilinogen, nitrates and leukocytes. These are not used in animals as they’re not specific to the species. It’s also worth mentioning that pH is more accurately measured with a pH specific dipstick.
- Pigment in the urine (for example with rabbit urine) can make the square panels almost impossible to read and may produce some wildly inaccurate results.
Did you know that its more reliable to drop urine onto each panel with a syringe than dip the stick?
E. Specific Gravity
SG is measured using a refractometer, which measures the degree by which light is refracted when it passes through a liquid. It’s directly proportional to urine osmolality, and depends on the number, size and weight of particles in urine. The loss of concentrating ability of the kidneys is among the first signs of renal tubular disease. Specific gravity in health will vary with the state of hydration and fluid intake.
Clinical conditions that can be identified using SG include;
- High specific gravity (>1.035) - nephrotic syndrome, dehydration, acute glomerulonephritis, heart failure, liver failure, or shock.
- Low specific gravity (<1.005) - diabetes insipidus, nephrogenic diabetes insipidus, acute tubular necrosis or pyelonephritis.
F. Urine Sediment
For the minimal amount of time it takes to prepare a urine sample to check the sediment, the results are usually well worth the effort. There are many factors that can influence the findings, so beware of interpreting the results without knowing the full story.