Wild Tiger Health Project
Created by Dr John C M Lewis

Urinalysis is performed to obtain information from urine samples. It is a valuable tool that provides information about the health and function of the urinary tract and also other body systems.

Urine samples can be collected free catch (preferable mid stream), cystocentesis, urinary catheterisation or from the floor. All these methods of urine collection are challenging in tigers. The best method for urinalysis is free catch and this is sometimes possible in a rehabilitation centre or captive environment when the tiger sprays. A sterile urine collection pot can be taped onto a stick and this used to remotely collect the sample. Often collection of urine from the animal’s environment may be the only feasible option. However, this method carries a high risk of contamination and are usually not reliable enough to test.

Samples should be collected into a clean sterile container with a secure, leak-proof lid, such as a yellow-top specimen jar. Ideally, urinalysis should be performed within one hour of collection to minimise artefactual changes. If immediate analysis is not possible, the sample should be refrigerated with the lid tightly secured to slow deterioration and preserve sample integrity during transport to an external laboratory.

There are various aspects to urinalysis:

Gross Examination of Urine

Before any specific testing is undertaken, a gross organoleptic assessment of the urine should be performed. This includes assessment of colour, odour, clarity, and turbidity.

As normal tiger urine is very concentrated it is usually not clear. It can range from yellow to light brown in colour. Colour intensity is influenced by urine concentration and volume and should therefore be interpreted in conjunction with urine specific gravity (USG) results. While abnormal urine colour may provide useful diagnostic clues, significant disease can still be present in urine that appears visually normal.

Common Urine Colour Abnormalities

Normal urine is generally transparent. Increased turbidity or cloudiness may result from the presence of cells, crystals, bacteria, mucus, lipid droplets, or other particulate matter. In some cases, turbidity may decrease following centrifugation as suspended particles settle into the sediment. Microscopic examination of the sediment can then be used to further investigate the underlying cause.

Urine specific gravity (USG)

Urine specific gravity should be measured using a refractometer. Urine SG can also be determined by using a urine dipstick but this is unreliable and is not recommended.

USG is one of the most valuable parameters assessed during urinalysis, as it provides information about the kidneys’ ability to concentrate or dilute urine in response to the body’s fluid requirements. Interpretation of USG should always be made in conjunction with the animal’s clinical status, hydration assessment, and other diagnostic findings.

Principle of Operation:

A refractometer measures the refractive index of a liquid. As the concentration of dissolved solutes increases, light passing through the sample is bent (refracted) to a greater degree. The instrument converts this measurement into a urine specific gravity reading.

Both analogue and digital refractometers are available. Analogue refractometers are generally preferred for field work due to their durability, simplicity, and independence from batteries or power sources.

Equipment Preparation and Calibration:

Accurate readings depend on proper cleaning and calibration.

1. Clean the prism and cover plate with distilled water and a soft, lint-free cloth or scratch-free tissue.
2. Place a few drops of distilled water on the prism and close the cover plate.
3. Hold the refractometer towards a light source and confirm the reading is 1.000.
4. If necessary, adjust the calibration screw according to the manufacturer’s instructions.
5. Calibration should be checked regularly, particularly after temperature fluctuations, transport, or periods of heavy use.

Procedure:

1. Collect a fresh urine sample in a clean container.
2. Allow refrigerated samples to return to room temperature before testing.
3. Place 1–2 drops of urine onto the prism surface.
4. Close the cover plate to spread the sample evenly across the prism.
5. Hold the refractometer horizontally towards a light source and look through the eyepiece.
6. Record the USG at the point where the light and dark fields intersect on the scale.
7. Clean the prism thoroughly with distilled water after use and return the instrument to its protective case.

Interpretation:

Urine specific gravity reflects both hydration status and renal concentrating ability.

• Hypersthenuric urine (high USG) indicates concentrated urine and is commonly associated with dehydration, reduced renal perfusion, or prerenal azotaemia.
• Hyposthenuric urine (low USG) indicates dilute urine and may occur with excessive water intake, certain endocrine disorders, or impaired renal concentrating ability.
• Isosthenuric urine  (urine concentration similar to plasma) in a dehydrated or azotaemic animal is abnormal and may indicate renal dysfunction.

Interpretation should always consider the patient’s hydration status. Dilute urine in a clinically dehydrated or azotaemic animal is of particular concern and warrants further investigation.

Reference Values for Tigers:

Published zoological data indicate that healthy tigers typically produce highly concentrated urine:

Values substantially below these ranges may indicate impaired concentrating ability, excessive water intake, recent fluid administration, or underlying disease.

Practical Considerations:

• Only a small volume of urine is required.
• Refractometer readings are generally more accurate than dipstick estimates of urine specific gravity.
• Temperature fluctuations can affect measurements, making regular calibration important.
• Grossly contaminated samples may produce inaccurate results.
• The prism should be cleaned after every use to prevent residue build-up and cross-contamination.

Refractometry provides a rapid, reliable, and non-invasive assessment of urine concentration and is an essential component of urinalysis in both field and clinical settings.

Factors Affecting Interpretation:

Urine specific gravity should always be interpreted within the context of the animal’s clinical condition and recent management history. Several factors can influence urine concentration independently of underlying renal function.

Recent administration of intravenous or subcutaneous fluids may temporarily reduce urine specific gravity by increasing hydration and promoting diuresis. Similarly, anaesthesia, sedation, and prolonged access to water can result in more dilute urine samples. Stress, diet, and the timing of sample collection may also influence urine concentration.

For this reason, a single USG measurement should not be interpreted in isolation. Whenever possible, results should be assessed alongside physical examination findings, hydration status, blood biochemistry, and the animal’s recent medical and husbandry history.

Dipstick tests

Urine dipstick testing is a rapid, inexpensive, and practical screening tool that can provide valuable information about urinary tract health, renal function, metabolic status, hydration, and systemic disease. Requiring only a small volume of urine, Multistix® strips are well suited to both hospital and field environments and can be easily incorporated into routine health assessments.

Available in a range of formats, Multistix® strips assess multiple analytes simultaneously, allowing a broad evaluation from a single urine sample. While dipstick results should always be interpreted alongside clinical findings and other diagnostic tests, they can provide useful screening information and help identify abnormalities warranting further investigation.

Advantages of urine dipstick testing include:

• Rapid results within minutes
• Minimal equipment requirements
• Ease of use in field conditions
• Low cost per test
• Ability to assess multiple parameters from a single sample

Storage and handling:

Dipsticks should be stored according to the manufacturer’s recommendations, typically in a cool, dry environment with the container tightly sealed. Expiry dates should be checked before use, as exposure to moisture, heat, or expired reagents can result in inaccurate results.

Procedure:

1. Collect a fresh urine sample in a clean container.
2. Wear gloves to minimise contamination and maintain appropriate OHS.
3. Apply urine to each reagent pad according to the manufacturer’s instructions, either by briefly immersing the strip or using a syringe or pipette.
4. Remove excess urine by gently tapping the edge of the strip against the container or blotting the side of the strip on absorbent material.
5. After the specified development time, compare each reagent pad with the manufacturer’s colour chart.
6. Record and interpret results in conjunction with the patient’s history, clinical examination, and other diagnostic findings.

Parameters commonly assessed:

Depending on the product used, dipsticks may assess up to ten parameters, including:

• Specific gravity: this test is inaccurate and a refractometer should be used)
• pH: usually 6-6.5 in tigers
• Protein: negative in a healthy animal (unless the urine is extremely concentrated)
• Glucose: negative in a healthy animal
• Ketones: negative in a healthy animal
• Leukocyte esterase: this test does not work in cats and the results of this should be discarded
• Bilirubin: negative in a healthy animal
• Urobilinogen: negative in a healthy animal. Interpret cautiously.
• Nitrite: negative in a healthy animal
• Blood (haemoglobin/myoglobin): negative in a healthy animal

Species considerations:

Although urine dipsticks are valuable screening tools, some reagent pads have limitations in veterinary species. In particular, the leukocyte esterase and nitrite tests have been shown to be less reliable in animals than in humans and should therefore be interpreted cautiously. False-positive and false-negative results are common, particularly in felids and wildlife species. Consequently, suspected urinary tract infections should not be diagnosed solely on dipstick results and should be confirmed through urine sediment examination, culture, and correlation with clinical findings where possible.

Clinical applications:

Abnormal dipstick results may assist in identifying or monitoring a range of conditions, including:

• Urinary tract disease – Nitrites, blood, and protein may indicate inflammation, infection, trauma, or other urinary tract pathology.
• Renal disease – proteinuria, haematuria, and alterations in urine concentration may suggest impaired kidney function.
• Diabetes mellitus – glucosuria and ketonuria may indicate inadequate glycaemic control.
• Liver disease – bilirubinuria and altered urobilinogen concentrations may indicate hepatobiliary dysfunction.
• Metabolic disorders – ketones and urine pH may provide insight into metabolic disturbances.
• Hydration status – urine concentration, particularly when interpreted alongside refractometer measurements, can assist in assessing hydration and renal concentrating ability.

Different strip formats are available. For example, Multistix® 10 SG strips evaluate up to ten parameters, whereas Multistix® 5 strips focus on a smaller number of key screening indicators, including glucose, nitrite, leukocytes, blood, and protein.

Urine sediment analysis

Microscopic examination of urine sediment provides valuable information regarding urinary tract health and can aid in the diagnosis of inflammation, infection, haemorrhage, crystal formation, and renal disease. Sediment examination is often performed alongside urine specific gravity and dipstick analysis to provide a more complete assessment of urinary tract function.

Procedure:

If a centrifuge and conical centrifuge tube are available:

1. Transfer approximately 3–5 ml of urine into a conical centrifuge tube.
2. Centrifuge at 1,000–1,500 rpm for 3–5 minutes.
3. Carefully decant the supernatant, leaving approximately 0.5 ml of urine with the sediment at the base of the tube.
4. Gently resuspend the sediment in the remaining fluid.
5. Place one or two drops of the suspension onto a clean glass slide and apply a coverslip.
6. Examine the preparation microscopically:
   • 100× magnification for casts, crystals and general sediment assessment.
   • 400× magnification for cells, bacteria, yeast and other microorganisms.

Possible Findings:

Sediment examination may reveal:

• Red blood cells
• White blood cells
• Epithelial cells
• Casts
• Bacteria, fungi or other infectious organisms
• Crystals *
• Lipid droplets
• Spermatozoa
• Mucus

The significance of these findings should be interpreted in conjunction with sample collection method, clinical signs, urine specific gravity, and dipstick results.

*Crystalluria

Crystals are commonly observed in urine sediment and may be physiological or pathological. Crystal formation is influenced by urine pH, urine concentration, temperature, storage conditions, and the time elapsed between collection and examination.

The presence of crystalluria does not necessarily indicate urolithiasis, and conversely, urinary calculi may be present in the absence of detectable crystals. For this reason, crystalluria should be interpreted cautiously and within the broader clinical context. In particular, struvite crystals can form in urine if some time has elapsed before it has been analysed.

Urine protein to creatinine ratio

The urine protein-to-creatinine ratio (UPC) is a quantitative assessment of urinary protein loss and is considered the preferred method for evaluating persistent proteinuria.

Because urine concentration can vary considerably between samples, measurement of urine protein alone may be misleading. The UPC ratio standardises protein concentration against urine creatinine concentration, providing a more reliable indication of protein loss.

Clinical Significance:

Proteinuria may occur secondary to:

• Glomerular disease
• Tubulointerstitial renal disease
• Systemic hypertension
• Inflammatory or infectious conditions
• Urinary tract haemorrhage
• Lower urinary tract inflammation

Persistent proteinuria may be an early indicator of renal disease and can occur before changes are detected on routine blood biochemistry.

Sample Collection and Submission:

A fresh urine sample should be collected in a clean container and submitted to a diagnostic laboratory. Cystocentesis samples are preferred where possible, although free-catch samples may be acceptable if significant haematuria or contamination is absent.

Urine should be refrigerated promptly and transported chilled according to laboratory requirements.

Interpretation:

UPC results should always be interpreted alongside urine sediment findings. Active urinary sediment containing blood, inflammatory cells, or bacteria may artificially increase urinary protein concentrations and lead to misleading results.

Persistent proteinuria confirmed on repeat testing is generally more clinically significant than an isolated abnormal result and may warrant further investigation of renal function and systemic disease.

In healthy cats, the urine protein to creatinine ratio (UP:UC) is usually <0.5.

Values between 0.5-1.0 in non-azotaemic cats are considered equivocal and continued monitoring for progression is recommended.

Values >1.0 in non-azotaemic cats are abnormal and diagnostic evaluation is warranted.

Urine culture

Urine culture is used to identify bacterial or fungal urinary tract infections and determine antimicrobial susceptibility. It is recommended when urinary tract infection is suspected based on clinical signs, urinalysis findings, or recurrent urinary tract disease.

Sample Collection:

To minimise contamination, urine submitted for culture should ideally be collected by cystocentesis. Free-catch samples may be acceptable in some circumstances but must be interpreted cautiously due to the potential for contamination from the lower urinary tract, genital tract, or surrounding skin.

Most laboratories require a minimum of 1 ml of urine collected into a sterile container or sterile plain tube. Requirements vary between laboratories and should be confirmed before submission.

Sample Handling:

• Collect urine aseptically whenever possible.
• Refrigerate immediately if transport will be delayed.
• Submit samples promptly with a cold pack.
• Avoid freezing unless specifically requested by the laboratory.

Interpretation:

Positive culture results should be interpreted in conjunction with clinical signs, sediment examination, and sample collection method. Organism identification and antimicrobial sensitivity testing can assist in selecting appropriate treatment.