Urine samples may be obtained by sampling during voluntary urination, by catheterisation, by direct puncture of the bladder or, if some contamination of the sample with faecal and other material is acceptable, by use of a metabolic cage. Metabolic cages designed for all of the common laboratory species are available commercially or may be manufactured “on-site” to meet particular requirements. If large volumes of an animal’s urine output are to be collected, a metabolic cage of the appropriate design should be used.
Sampling during voluntary urination is occasionally useful in laboratory rodents and dogs and cats. When rats and mice are picked up and restrained, they frequently urinate, and this may be taken as an opportunity to collect small volumes of urine for analysis. Samples will be contaminated with small amounts of faecal material, cells and bacteria from the genital tract, skin, hair and other debris, but may be useful for some purposes.
Cats may often be persuaded to urinate by applying gentle manual pressure to the bladder through the body wall. Once again, the sample will be contaminated with debris, but prior cleaning of the perineum may minimise this.
Dogs will often urinate when removed from their pens to an exercise area, although as with other species, samples obtained during voluntary urination usually have some degree of contamination.
Urethral catheterisation is used routinely in the larger species – the rabbit, cat and dog, but is also relatively easy to carry out under general anaesthesia in female rats and mice.
In all species, care must be taken to minimise the risk of introducing infection into the urinary tract during the procedure. Catheters must be sterilised before use, as should any lubricating gels and specula.
Cystocentesis, or direct puncture of the bladder through the body wall, is possible in most species, but practicable as a routine procedure only in larger animals. The bladder must be palpable to enable accurate insertion of the sampling needle, limiting this procedure to rabbits and larger species. This procedure normally requires anaesthesia.