sugar solutions and the lower specific gravity of zinc sulfate solutions can impede the passive flotation process (Zajac and Conboy 2012). In the absence of centrifugation or proper flotation solutions, the likelihood of inaccurate test results warrants consideration of additional diagnostic testing or empirical treatment of patients exhibiting clinical signs consistent with parasitic infection.
Once the sample is prepared and the surface layer transferred to a coverslip, the sample should be scanned under the 10× objective lens of a microscope. To maximize the contrast between parasites and background debris, the microscope condenser should be lowered and the light intensity and diaphragm should be reduced. Samples prepared in sodium nitrate solution should be evaluated immediately to avoid distortion of any parasites and crystallization of the preparation (Bowman 2014; Zajac and Conboy 2012).
4.3.2.4 Urinalysis
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.
4.3.3 Secondary Diagnostic Testing
4.3.3.1 Complete Blood Count and Blood Chemistry Analysis
Along with a urinalysis, a complete blood count and blood chemistry analysis are typically considered part of the minimum metabolic database allowing the practitioner to gain an overall assessment of a patient's ability to oxygenate the body, respond to infection or inflammation, and perform the most basic organ functions (Table 4.3). Complete blood counts should include both a quantitative analysis (i.e. a count of the number of cells of a particular type) as well as a qualitative analysis (i.e. microscopic evaluation of cellular morphology in a blood smear). Quantitative analysis is typically performed by automated hematology analyzers, though manual counts can be obtained through the use of a hemocytometer. If neither automated nor manual counts are feasible, assessment of packed cell volume (PCV) is a readily available means of assessing the degree of anemia and the oxygen‐carrying capacity of the blood and can be combined with a simple blood smear for a more thorough assessment. The PCV represents the percent of the patient's total blood volume comprised of red blood cells and is directly measured after centrifugation of a sample. Though a measure of the same parameter, a patient's hematocrit (Hct) is calculated based on the red blood cell count and cell volume. Agglutination of red blood cells or inclusion of platelets in the count will, therefore, impact the Hct but not the PCV. Normal PCV values are 37–55% for dogs and 26–45% cats. An additional benefit of obtaining a PCV is the ability to subjectively assess plasma and measure protein concentrations (see below). Qualitative analysis of red and white blood cells can be assessed by microscopic examination of the long or “feathered” edge of a blood smear. Examination after air‐drying and staining with a Romanowsky stain can enhance the diagnostic value. Cells should ultimately be examined under the 100× objective with oil immersion and should be assessed for color, size, shape, inclusions in red blood cells (e.g. Howell‐Jolly bodies, Heinz bodies, basophilic stippling) and signs of toxicity in white blood cells (e.g. basophilia, vacuolation, Döhle bodies). A variety of infectious agents may also be identified in both red blood cells (e.g. Mycoplasma spp., Babesia spp., and Cytauxzoon) and white blood cells (e.g. intracellular bacteria, Ehrlichia spp., Anaplasma spp., Hepatozoon spp.). Viral inclusion bodies of canine distemper virus can also occasionally be seen within red blood cells and within the cytoplasm of white blood cells (Rosenfeld and Dial 2010d; Webb and Latimer 2011). Finally, particularly when subjected to centrifugation methods, microfilaria of D. immitis may also be identified on blood smear analysis.
Blood chemistry analysis may include a variety of parameters to assess the function of major organ systems (e.g. renal, hepatic), total proteins, electrolytes, and metabolism of carbohydrates and lipids. These assessments are most thoroughly and accurately performed through the use of calibrated, automated biochemical analyzers either in‐house or at a diagnostic laboratory. If complete biochemical profiling is not available, crude assessments of total proteins, blood urea nitrogen (BUN), and blood glucose can be conducted in almost any setting.
As mentioned above, after obtaining a PCV, an analysis of the remaining plasma can easily be undertaken. Plasma color and transparency should first be visually assessed. For both dogs and cats, plasma is normally clear and colorless; yellow plasma indicates icterus, pink or red indicates hemoglobinemia, and white to pink opaque plasma indicates lipemia. Finally, the plasma sample
