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Urinalysis is useful for the evaluation of renal function, assessment of urinary tract diseases, and the analysis of systemic disease processes that impact the urinary system. There are four main diagnostic tests utilized to evaluate the urinary system: urine specific gravity, urine chemical analysis (i.e. use of reagent strips or “dipstick”), urine sediment analysis, and urine culture (Table 4.3). Urine sediment analysis and urine culture are of the most utility regarding the diagnosis of infectious diseases, though direct testing may be warranted under certain circumstances (e.g. canine distemper virus, leptospirosis).

Analysis of urine sediment can aid in the diagnosis of bacterial, fungal, algal, and parasitic diseases of the urinary tract. The sample should be obtained through cystocentesis or catheterization in order to confirm that any pathogens identified originate in the kidneys or bladder. If that is not feasible, a midstream voided urine sample can be utilized to minimize contamination from the urethra and external environment. After obtaining the specific gravity and urine chemical analysis, the sediment can be prepared for microscopic evaluation through low‐speed centrifugation (1,500–2,000 RPM for 5 minutes), decanting of the supernatant, resuspension, and preparation on a glass slide. Both unstained and stained drops of urine should be evaluated for cells, casts, crystals, and infectious organisms. Fat droplets, spermatozoa, mucous, and other contaminants may also be identified. Preparations can be stained with a Romanowsky stain after drying for detailed identification of cellular elements and examination under oil immersion; however, crystals will be dissolved by the fixative component. Supravital stain (e.g. Sedi‐Stain) or new methylene blue can be applied to a wet‐mounted sample if preservation of crystals is desired; however, cellular detail is lost, examination under oil immersion is not possible, and accumulation of bacteria and stain precipitate resulting in sediment artifacts are common (Anthony 2014). The presence of more than five white blood cells per high‐power field indicates urogenital tract inflammation and the sample should be carefully evaluated for the presence of bacteria (Tripathi et al. 2011). Bacteria in the absence of white blood cells could indicate contamination of the sample during collection or processing. Both rod and coccoid bacteria can be found, with progressively motile rods being the most common. Yeast are the most common fungal organisms identified and are usually contaminates from the lower urinary tract (Rosenfeld and Dial 2010c).

A large number of bacterial organisms in the presence of red and/or white blood cells along with clinical signs of urinary tract disease are an indication for bacterial culture with antimicrobial sensitivity. Alternatively, a rapid immunoassay has been evaluated for point‐of‐care diagnosis of urinary tract infections (UTIs) in dogs and found to be highly accurate (Jacob et al. 2016). The most common organisms identified in bacterial cultures of dogs and cats include Escherichia coli, Klebsiella spp., Staphylococcus spp., Enterococcus spp., Proteus spp., and Pseudomonas spp. with E. coli accounting for up to 55% of isolates (Thompson et al. 2011). The International Society for Companion Animal Infectious Diseases recommends the use of amoxicillin or trimethoprim‐sulfonamide for first‐line antimicrobial treatment of uncomplicated UTIs and only when such infections are deemed to be clinically significant, as defined by the presence of clinical signs such as dysuria and pollakiuria, along with the identification of bacteria in the urine (Weese et al. 2011). Antimicrobial resistance to fluoroquinolones, third‐generation cephalosporins, and clavulanic acid‐potentiated β‐lactams are increasingly reported, so their use should be limited to those cases in which resistance to first‐line antimicrobials has been documented (Thompson et al. 2011; Weese et al. 2011). Animals that have been empirically treated for a UTI that has not resolved should have a urine culture performed at a diagnostic laboratory.