17 Aug 2015
Sarah Caney
Job Title
Figure 2. Free catch urine sample collection: once the cat has urinated, the tray is tipped and the sample collected.
Urinalysis is an essential component of patient assessment. In general, especially for sick cats, cystocentesis is the preferred method for urine collection as it facilitates rapid, sterile sampling and the sample is suitable for all types of urinalysis. Urine samples can be obtained from conscious cats with minimal restraint.
Free catch samples are entirely acceptable for initial screening tests, but may be “contaminated” by cells, protein and bacteria in the urethra/genital tract and litter tray, and this can affect interpretation of some test results.
Table 1 summarises the “ideal” sample requirements, although it is important to emphasise free catch samples can still be submitted for bacteriology, urine protein to creatinine ratio and so on – it is just the interpretation that may be more complicated.
Before proceeding to collect a sample, it is worth remembering general cat-friendly tips since the more relaxed the cat is, the easier it will be to sample.
The only requirements for successful sampling are a calm cat whose bladder can be palpated. The author prefers to use a 1in 23-gauge needle and a 5ml or 10ml syringe. The patient is restrained as gently as possible standing, in lateral recumbency or in dorsal recumbency. In general, it is best to have the cat in the position in which it feels most comfortable. If the cat becomes tense, the bladder will be much harder to palpate, so it is in your interest to keep the cat as calm and happy as possible.
When restraining cats in dorsal recumbency, it is sometimes helpful to have two assistants – one at each end, gently holding one limb in each hand to keep them out of your way. The cat should be restrained on a deep, soft bed to add to its comfort. There is no need to clip the fur or aseptically prepare the skin prior to cystocentesis.
The bladder is palpated and stabilised with one hand while the other hand is used to manipulate the syringe. If the cat is lying on its back, the bladder can be pushed caudally so it is stabilised between your hand and the bones of the pelvis (Figure 1). If the cat is standing or lying on its side, the bladder can be stabilised so your thumb is at the cranial pole and your fingers gently lift the bladder towards you.
Once the bladder is stabilised, the needle guard should be removed and the needle placed gently on to the skin over the bladder. By resting the needle on the skin before slowly sliding through, most cats will not appear to feel anything and won’t be startled. The needle is passed all the way through the skin so the needle hub is sitting on the skin. The urine is aspirated with one hand and then pressure is released with the other before withdrawing the needle.
Adverse effects of cystocentesis are very rare in healthy cats, but include bruising and haemorrhage (usually microscopic, but may affect urinalysis results), transient vagal stimulation (retching, panting and collapse), urine leakage and bladder rupture (seen rarely in cats with urethral obstruction).
If the bladder is not palpable, but cystocentesis is very desirable (for example, when a urine culture is needed), ultrasound can be used to locate the bladder and guide the needle.
Again, there is no need to clip the fur. A good quantity of ultrasound gel is applied to the area before imaging and sampling, taking care not to introduce the needle through the gel or through the tip of the probe.
Initial urine assessment can be done using a free catch urine sample brought in by an owner, or collected in the practice. To collect a free catch sample from a cat, the patient is confined with an empty litter tray or one containing non-absorbent cat litter.
Once the cat has urinated, a urine sample is collected using a pipette or syringe and placed into a sterile tube for subsequent analysis (Figure 2). Free catch sampling can affect urinalysis results – especially bacterial culture, sediment examination and protein assessment.
It is important to emphasise bacteriology, sediment and protein assessment can still be diagnostic when evaluating a free catch sample, so this should not be a barrier to performing these tests if it is not possible to collect a cysto sample.
If fewer than 1,000 colony forming units per ml (CFU/ml) are cultured from a free catch sample, and especially if a mixture of common commensal bacteria are reported, then it is likely this represents contamination rather than a urinary tract infection.
Numbers greater than this (and especially if greater than 10,000CFU/ml, single bacteria cultured) are likely to be significant. If collected with the cat at home, the owner should be advised to bring in the sample as soon as possible for analysis.
Other techniques for urine sample collection include the following.
A summary of in-house urinalysis findings are in Table 2.
Technical and video guides to cystocentesis and owner collection of urine samples are available on the author’s website: www.vetprofessionals.com/catprofessional/free_downloads.html
