Urinalysis is an important veterinary diagnostic tool to detect health conditions such as chronic kidney disease, urinary tract infections, or diabetes in companion dogs and cats. However, diagnostic variables exist that need to be considered and that could contribute to inaccurate results.
Variables
A) Time of collection
B) Time between collection and analysis
C) Method of collection
D) Diagnostic tools to analyze sample
Within that framework, veterinarians need to consider the preferred (ideal) method, emergency situations, and the exceptions that could apply.
First, what does a complete urinalysis entail?
Urinalysis
Additional screening tests can be done using urine. Listed below is what veterinarians typically look for to diagnose or eliminate diseases at the beginning.
1) Color
2) Odor
3) Turbidity (cloudiness)
4) Volume
5) pH (high alkaline or low acid?)
6) Specific gravity
7) Protein
8) Glucose
9) Ketones
10) Blood
11) Erythrocytes (red blood cells)
12) Leukocytes
13) Neutrophils (white blood cells)
14) Epithelial cells
15) Casts
16) Crystals
17) Microorganisms
18) Abnormal or neoplastic (cancer) cells
Time of Collection
The preferred time of collection is the first urination in the morning, before any exercise.
Time between Collection and Analysis
The time between collection and analysis ideally should be less than one hour, unless the sample is refrigerated. If it is longer than that or not stored properly, the urine sample gradually degrades and this could lead to inaccurate results.
Method of Collection
Three types of collection exist:
A) Free catch – Involves placing a container under the companion dog or cat while they urinate. This is the least invasive but often the least accurate method.
B) Catheterization – Placing a urinary catheter up the urethra and into the bladder. This is invasive and can cause irritation to the urethra and bladder wall.
C) Cystocentesis – A minimally invasive procedure that collects urine directly from the bladder using a needle and syringe. This is the preferred and most accurate method, especially if performed with an ultrasound-guided probe to pinpoint the bladder.
Diagnostic Tools to Analyze Sample
Common diagnostic tools are:
A) Dipstick/reagent strips
B) In-house chemistry analyzer (veterinary clinics or hospitals might have several analyzers that perform different functions for urinalysis)
C) Pick up by a local veterinary reference laboratory courier for their analysis
Preferred Method
Once we combine all of the variables above and weight them compared to the other variables, cystocentesis is the preferred method of collection as is sending the urine sample to a veterinary reference laboratory.
Why? Because free-catch samples from a household have too much variability due to sample contamination. For instance, a “clean” plastic container is not sterile. Detergent in trace amounts may be present in the container and will skew the results. The free-catch samples then can be positive for red and white blood cells, bacteria, etc., and in order to measure the protein level and pH accurately, the urine will still need to be sampled via cystocentesis.
As stated earlier, cystocentesis is minimally invasive.
Reagent strips can either be interpreted by a trained professional or with an automated test strip analyzer. However, since the color changes can be subtle, diagnoses could vary between interpreters.
The automated test strip analyzers are slightly more accurate, but a 2021 study out of South Korea demonstrated that one of them was not as precise in measuring the urine protein:creatinine ratio as the wet or dry analyzers.
Overall, the studies completed thus far to verify the accuracy of test strips and the associated diagnostic tool have reached conflicting conclusions. Further, the test strips could be outdated, which can lead to inaccurate results, especially with regard to glucose. In fact, veterinarians and healthcare professionals should not use test strips for urine specific gravity, urobilinogen, nitrite or leukocytes.
Emergency Situations
We understand that extenuating circumstances occur that necessitate an immediate diagnosis. For instance, your companion pet is not eating, urinating or defecating, or has vomiting or diarrhea.
In this instance, we would prefer cystocentesis for urine retrieval. If your companion pet is too stressed for it, free catch with a sterile container by the veterinary staff is preferred. Then, it should be run with an in-house analyzer.
Once the patient is stable, repeating another round of urine tests one to two weeks afterwards is usually needed.
Exceptions
One important exception is when we collect urine to measure the urine cortisol:creatinine ratio (UC:CR). First thing in the morning urine is required and collected by the companion pet parent. Why?
Cortisol is released by the body’s adrenal glands during any stress situation including the fight-or-flight response or exercise throughout the 24-hour day. If cortisol is elevated in urine, it can be an indicator of Cushing’s Disease (hyperadrenocorticism). Taking a urine sample at that time will show if the cortisol is higher than the reference baseline as compared to the creatinine. Any other retrieval time or place like a veterinarian’s office will lead to a stress/excitement-induced elevated urine cortisol, and an inaccurate result.
If your veterinarian requests a urine sample to measure UC:CR, please get a sterile container from them.
Additionally, dogs that are small enough should be carried outside to collect the first morning urine sample.
References
Cridge, Harry et al. “Correlation between urine color and urine specific gravity in dogs: Can urine color be used to identify concentrated urine?” The Canadian veterinary journal = La revue veterinaire canadienne vol. 59,2 (2018): 178-180, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5764211/.
Harley, Leyenda, and Cathy Langston. “Proteinuria in dogs and cats.” The Canadian veterinary journal = La revue veterinaire canadienne vol. 53,6 (2012): 631-8, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3354822/.
Ji, Sumin et al. “Comparison of three types of analyzers for urine protein-to-creatinine ratios in dogs.” Journal of veterinary science vol. 22,1 (2021): e14. doi:10.4142/jvs.2021.22.e14, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7850794/.
Mie, Keiichiro et al. “Evaluation of the accuracy of urine analyzers in dogs and cats.” The Journal of veterinary medical science vol. 81,11 (2019): 1671-1675, doi:10.1292/jvms.18-0468, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6895637/.
Mösch, Martina et al. “Influence of preanalytic and analytic variables in canine and feline urine specific gravity measurement by refractometer.” Journal of veterinary diagnostic investigation: official publication of the American Association of Veterinary Laboratory Diagnosticians, Inc vol. 32,1 (2020): 36-43, doi:10.1177/1040638719896785, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7003217/.
Rizzi, Theresa E. Urinalysis in Companion Animals, Part 1: Collection, Sample Handling, & Initial Evaluation. Today’s Veterinary Practice, 22 Oct. 2019, https://todaysveterinarypractice.com/todays-technician-urinalysis-in-companion-animals-part-1-collection-sample-handling-initial-evaluation/.
Rizzi, Theresa E. Urinalysis in Companion Animals, Part 2: Evaluation of Urine Chemistry & Sediment. Today’s Veterinary Practice, 22 Oct. 2019, https://todaysveterinarypractice.com/urinalysis-in-companion-animals-part-2-evaluation-of-urine-chemistry-sediment/.
Yadav, S N et al. “Urinalysis in dog and cat: A review.” Veterinary world vol. 13,10 (2020): 2133-2141. doi:10.14202/vetworld.2020.2133-2141, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7704312/.