Urine collection

Urine collection in dogs and cats (2013)

Alexander Hüttig and The IRIS Board

The goal of a urine collection procedure is to obtain the highest quality urine sample with lowest risk of complications to the patient. The method of collection, collection container used, the interval between collection and analysis, and the method of handling of the sample in this interval are all important aspects of the process, as these will affect both the results and the interpretation of the results obtained. Furthermore, the volume of urine collected is another important consideration. The usual goal is to collect at least 5 mL to enable determination of urine specific gravity, dipstick chemistries, sediment examination and storage of a portion of the urine in case the initial results of the urinalysis lead to further diagnostics tests, such as measurement of the urine protein-to-creatinine ratio or an aerobic bacterial urine culture.

There are at least four ways to obtain urine from the bladder:

  • Natural voiding
  • Manual compression of the bladder
  • Transurethral catheterization of the bladder
  • Cystocentesis

Natural or normal voiding

If the owner brings you a voided urine sample from the patient, this offers potential advantages– firstly, if the sample is usable it reduces risks of potential complications or infection that could result from a second sampling by a different method and, secondly, acceptance and use of the offered sample will encourage the involvement and compliance of the owner in case management. There are useful methods of collection of voided samples (e.g., use of inert kitty litter in a clean litter box or collection of canine urine directly into a clean container during voiding) and inherently unreliable methods of collection (e.g., collection of urine from a dirty litter box or scooping urine from the floor). Further, the time interval between collection and delivery of the sample and the method of sample handling in the interim (e.g., refrigerated or held at room temperature) are also key factors in judging the usability of the sample.

All voided samples are assumed to be contaminated with bacteria, cells, and debris from the genitourinary tract or skin and hair. However, they may be satisfactory for screening purposes, such as determination of urine specific gravity, dipstick analysis, and determination of the urine protein-to-creatinine ratio particularly if the sample was collected, handled and stored properly, and the urine sediment examination is normal. If a potential abnormality is found on dipstick analysis or urine specific gravity measurement, it is often preferable to confirm and follow-up this finding by first obtaining a urine sample by another means in order to avoid the risk of false positive findings. In almost all cases, a voided sample is considered unsatisfactory if bacterial culture is being considered.

Manual compression of the urinary bladder

On occasion, this can be very useful if the patient is small, generally <12 pounds (<5.5 kg), and is calm and compliant. However, the urinary bladder can be traumatized if excessive digital pressure is applied, it is painful to some patients (especially those with lower urinary tract disease), and this procedure may lead to misinterpretation if haematuria results from the procedure. Furthermore, urine (potentially contaminated with bacteria) may be forced into the prostate gland or ureters, renal pelvis and renal parenchyma if bladder compression is not accompanied by simultaneous relaxation of the urethral sphincter. Because of technical challenges inherent to this method and the attendant risk to the patient, this method is not recommended for most situations where a urine sample is desired.

Transurethral catheterization

In the authors' opinion, catheterization of the urethra solely to collect a urine sample is best avoided. There is a risk of iatrogenic bacterial infection, even when the procedure is performed in a seemingly aseptic and atraumatic fashion, as passage of the catheter invariably transports bacteria from the distal urethra into other areas of the urinary tract (e.g. prostate gland or urinary bladder). Urine samples obtained by this method are often contaminated with bacteria and cells from the distal urethra and adjacent tissues, complicating interpretation of bacterial culture and sediment examination.

Diagnostic cystocentesis

Needle puncture of the urinary bladder to collect the required amount of urine has advantages to the patient and aids interpretation of test results. In general, cystocentesis is better tolerated than catheterization, and there is less risk of introducing an iatrogenic infection than with catheterization. It also avoids contamination of urine samples with bacteria, cells and debris from the lower urogenital tract, thereby facilitating interpretation of results and assisting localization the sources of haematuria, pyuria and bacteriuria. For aerobic bacterial culture of urine, this is by far the best method of sample collection as a properly collected cystocentesis sample should be expected to be sterile.

Passage of the needle through the bladder wall can cause microhaematuria, especially if cystitis is present. Typically this results in <20 red blood cells per high power field in the sediment examination but no other artifactual findings in the urinalysis. To avoid escape of urine into the abdomen, some recommend that the needle be directed at a 45 degree angle through the bladder wall, rather than at a right angle to it. This approach will create an oblique pathway that should close immediately as the needle is withdrawn.

Many veterinary practitioners prefer to perform cystocentesis with the animal restrained exactly upright in dorsal recumbency. Others prefer to restrain the animal in lateral recumbency and still others prefer to perform this procedure in a standing animal. The size and compliance of the patient could play a role in the selection of approach.

Regardless of animal position, antiseptic treatment of the skin is performed first, then the needle is inserted through the skin and the ventral bladder wall, where there is less risk of touching large vessels or the ureters.

In female dogs, and both sexes in cats, the needle is inserted through the linea alba or the lateral abdominal wall. For male dogs a paramedian site is chosen, close to the penis, after first evaluating the size of the prostate to avoid contacting an enlarged gland. Use of ultrasound guidance is recommended if a prostatic cyst is suspected.

If the bladder cannot be palpated for some reason (e.g., low urine volume, adiposity, oedema, abdominal splinting), the use of ultrasound guidance should be considered, if available. If there is any doubt, or for inexperienced clinicians, ultrasound guidance will provide more confidence with the process. For the ultrasound-guided method of cystocentesis, a syringe may be used, but some prefer to use a Becton, Dickinson's Vacutainer™ device. Singlehanded sample collection is then possible, the other hand being used to manipulate the ultrasound probe. This avoids environmental contamination and the vacuum tube remains closed until the sample is analysed. Use of boric acid tubes to collect urine where bacterial culture is required can lead to false negative cultures.

Is there a preferred time for urine collection?

A urine sample can be collected at any time, particularly for screening analysis. However, urine characteristics may vary throughout the day. To facilitate interpretation of results, it is helpful to record both the timing of urine collection and whether the animal was fasted or was recently fed. Likewise, the time between recent water intake and urine collection can be relevant if urine specific gravity is being used to assess kidney function. Any delay between collection and analysis should be minimized to minimize in vitro changes.

Early morning fasting urine samples

This is the best sample to use when evaluating renal function - it follows the longest period of fasting and likely low water intake, so the urine specific gravity may better reflect the patient's urine concentrating ability.

Recently formed urine samples

Cytological details may be superior with freshly formed urine, as compared with samples stored in the bladder for a longer time. Fresh samples may be less concentrated than morning samples and so provide a less optimal estimate of urine concentrating ability.

Overview of urine collection

In summary, the method of collection and handling of a urine sample is critical to proper interpretation of the urinalysis. Ideally, this means an early morning urine sample in a fasted patient that is collected by cystocentesis and analyzed shortly (<1 hour) after collection by determination of the urine specific gravity, dipstick chemistries, and urine sediment examination. A portion of the urine should be aseptically stored (20C for 1-3 days) in case subsequent analyses, such as aerobic urine culture or determination of the urine protein-to-creatinine ratio, are deemed appropriate.

Further Reading

Albasan H, Lulich JP, Osborne CA, et al. Effects of storage time and temperature on pH, specific gravity, and crystal formation in urine samples from dogs and cats. J Am Vet Med Assoc 2003;222:176-9.

Beatrice L, Nizi F, Callegari D, et al. Comparison of urine protein-to-creatinine ratio in urine samples collected by cystocentesis versus free catch in dogs. J Am Vet Med Assoc 2010;236:1221-4.

Reine NJ, Langston CE. Urinalysis interpretation: how to squeeze out the maximum information from a small sample. Clin Tech Small Anim Prac 2005;20:2-10. van Duijkeren E, van Laar P, Houwers DJ . Cystocentesis is essential for reliable diagnosis of urinary tract infections in cats. Tijdschr Diergeneeskd 2004;129:394-6.

Zatelli A, Paltrinieri S, Nizi F, et al. Evaluation of a urine dipstick test for confirmation or exclusion of proteinuria in dogs. Am J Vet Res 2010;71:235-40.