Despite the availability of new diagnostic tests, some older tests still provide valuable information that can be used to diagnose, monitor, and treat many conditions.<\/p>\n
Although most are simple to perform, some require training to both perform and interpret. Costs vary, but most are inexpensive. The practicality and usefulness of these diagnostic tests should not be overlooked.<\/p>\n
Take-Home Points<\/strong><\/p>\n As we navigate the rapid development and transformation of veterinary medicine, diagnostic tests are continuously emerging and evolving. Although these newer tests can be valuable and relevant resources, they often provide a narrow spectrum of information attached to a sizable price tag. As newer diagnostic tests become available, many older, practical, and affordable tests may be overlooked. Performing and interpreting these diagnostics are critical skills as these tests can provide comprehensive diagnostic, monitoring, and treatment information. This article provides cost (<\/span>BOX 1<\/b><\/span>), indications, methods, and interpretation for several key practical and cost-effective diagnostic tests.<\/span><\/p>\n Blood smears are a fundamental part of a complete blood count (CBC). Although smears are inexpensive, training is required to prepare good quality slides, analyze them, and interpret the findings (<\/span>BOX 2, FIGURE 1<\/b><\/span>). A well-prepared blood smear remains paramount for:<\/span><\/p>\n Cost:<\/b> <\/span>$<\/span><\/p>\n Materials needed:<\/b> Microscope slides, Diff-Quik stain (Romanowsky stain variant), microscope with 4\u00d7 to 100\u00d7 objective lenses, immersion oil<\/span><\/p>\n Methods and interpretation: <\/b>Evaluating blood smears requires a systematic approach. To assess the quality of the smear, the authors recommend initial evaluation under low magnification, followed by assessment of the density of RBCs and WBCs (10\u00d7 to 20\u00d7 objective). Slides are also assessed for rouleaux formation and\/or agglutination. Under the same objective, the feathered edge is assessed for platelet clumps, microfilaria, or any large abnormal cells (e.g., blast cells, mast cells, macrophages).<\/span><\/p>\n Figure 1. Blood smears. (A) Properly performed; (B) too much blood; (C) too little blood.<\/p><\/div>\n To approximate hematocrit, monolayer examination of <\/span>RBC apposition may be used. In anemic patients, RBCs are widely separated from one another; in nonanemic patients, RBCs are closely apposed (<\/span>FIGURE 2<\/b><\/span>). These estimates should be referenced against measured hematocrit or packed cell volume (PCV).<\/span><\/p>\n Figure 2. Red blood cell density. (A) Sample from healthy patient, normal density, at 20\u00d7 objective. Courtesy University of Florida Clinical Pathology Department<\/p><\/div>\n Figure 2. Red blood cell density. (B) Sample from anemic patient (packed cell volume 17%) at 20\u00d7 objective. Courtesy University of Florida Clinical Pathology Department<\/p><\/div>\n To approximate WBC counts under the 10\u00d7 objective, count the number of WBCs in the monolayer (usually 18 to 50 cells). Each WBC corresponds to 330 cells\/\u00b5L. For example, 13 WBCs\/10\u00d7 objective; 13 \u00d7 330 cells\/\u00b5L = 4290 WBCs\/\u00b5L. The number of cells per \u00b5L = (average no. cells\/field) \u00d7 (objective power).1<\/sup><\/span><\/p>\n A more definitive assessment of RBCs, WBCs, and platelets can be performed under higher power (100\u00d7 objective). More specifically, a manual differential cell count can be performed to verify hematology analyzer results, concurrently assessing morphology, density, and presence of inclusion bodies or parasites (<\/span>TABLE 1, FIGURES 3 AND 4<\/b><\/span>). At 100\u00d7 magnification, a platelet count can also be performed. Platelets over several fields (5 to 10\/field) are counted and then averaged. The average platelet number is then multiplied by 15<\/span>\u2009<\/span>000 to 20<\/span>\u2009<\/span>000 to estimate platelets\/\u00b5L (<\/span>FIGURE 3<\/b><\/span>).<\/span><\/p>\n Figure 3. Feline blood smear with numerous Heinz bodies (arrows) at 100\u00d7 objective. Approximately 7 platelets can be seen. If this is an accurate representation of platelet numbers within several fields, 7 \u00d7 15\u2009000\u201320\u2009000 gives an estimated platelet count of 105\u2009000\u2013140\u2009000 platelets\/\u00b5L. Courtesy University of Florida Clinical Pathology Department<\/p><\/div>\n Figure 4. Blood smear from feline patient with cytauxzoonosis; 100\u00d7 objective. Note numerous small piroplasms in RBCs (arrows). Courtesy University of Florida Clinical Pathology Department<\/p><\/div>\n This test is underutilized in veterinary medicine. When performed and interpreted correctly, the test provides valuable information for disease diagnoses and assists clinicians with medically guided treatment. <\/span><\/p>\n Cost:<\/b> <\/span>$<\/span><\/p>\n Materials needed:<\/b> Determining PCV requires microhematocrit tubes, clay sealer, a microcentrifuge, a refractometer<\/a>, and a PCV reading tool.<\/span><\/p>\n Methods and interpretation:<\/b> PCV should always be interpreted in conjunction with total protein and assessed with patient history, clinical examination findings, and other diagnostic test results when available (<\/span>TABLE 2<\/b><\/span>). Reference ranges are 37% to 55% for adult dogs (most breeds) and 30% to 45% for cats. PCV is lower in young animals (4 weeks; 24% to 34%) than in adult animals and gradually increases with maturity.1<\/sup><\/span><\/p>\n Microhematocrit tubes also provide valuable information after blood is centrifuged and separated into layers. <\/span><\/p>\n Figure 5. Blood-filled microhematocrit tubes after centrifugation. Note the red discoloration of plasma in the sample on the left, suggestive of free hemoglobin. The buffy coat (arrow) is easily visualized between the red blood cells and plasma.<\/p><\/div><\/li>\n Complete urinalysis results play a vital role in evaluating urinary tract health and provide valuable information about the systemic wellness of patients. Urinalysis should be interpreted in conjunction with patient history and physical examination findings and is indicated for any patient having blood collected for a CBC and serum chemistry. Likewise, urine should be analyzed for patients that are systemically ill or have renal disease. <\/span><\/p>\n Cost:<\/b> <\/span>$<\/span><\/p>\n Materials needed<\/b>: Refractometer, urine dipstick, centrifuge, pipette or syringe, conical or red top tube, microscope slides, microscope with 4\u00d7 to 100\u00d7 objective lenses, and immersion oil<\/span><\/p>\n Methods and interpretation:<\/b> Urine can be collected by free catch, catheterization, or cystocentesis. Recording both the method and time of collection is recommended as these factors may affect results. Early morning urine samples are considered best for evaluating tubular function, whereas late morning to early evening samples are best for microbial culture and assessing cellular morphology.3,4<\/sup> To avoid temperature- and time-dependent effects on crystal formation, samples should be analyzed within 1 to 2 hours of collection3<\/sup>; if not analyzed during this window, samples should be refrigerated. <\/span><\/p>\n Assessment involves evaluation of physical characteristics, semiquantitative chemical analysis, and sediment.<\/span><\/p>\n Dry reagent strips are used in veterinary medicine to <\/span>determine urine pH, protein, glucose, ketones, bilirubin\/urobilinogen, and occult blood. Tests pads produce a colorimetric chemical reaction when interacting with <\/span>specific substances in urine.8<\/sup> Reagent strips are unreliable for measuring USG, WBCs, nitrite, and urobilinogen.9<\/sup> Pigmented urine can interfere with test strip readings. Urine pH, a global estimate of acid\u2013base status, may be affected by many renal and extrarenal factors (e.g., handling, diet, medications, bacterial infection, systemic illness).5,10<\/sup> Glucosuria, when detected, should be assessed concurrently with <\/span>serum glucose.11<\/sup> Determining protein concentration by dipstick, which primarily detects albumin, is a good screening test for proteinuria<\/a>. Results must be interpreted in light of USG, pH, and urine sediment examination.5<\/sup> Negative reactions are usually reliable; samples with positive test reactions for patients with an inactive urine sediment should undergo quantitative confirmatory testing (i.e., urine protein:creatinine [UPC] ratio). <\/span><\/p>\n Sediment provides definitive evidence of inflammation, infection, or hemorrhage within the urinary tract.5<\/sup> Samples are centrifuged at low speed (1000 to 1500\u00a0rpm) for 5 minutes before most of the supernatant liquid is removed, leaving the sediment and a small volume (0.5 to 1 mL) of urine. The sample is then resuspended and 1 drop is placed on a microscope slide with a coverslip. Slides are analyzed at low power for crystals and casts and at high power for cells (RBCs, WBCs, transitional cells) and bacteria. Crystalluria is a common finding; certain crystals (e.g., amorphous, struvite) can be seen in healthy dogs.12<\/sup> More information on slide preparation and analysis is available in the Today’s Veterinary Practice<\/i> May\/June 2014 article, Urinalysis in Companion Animals, Part 2: Evaluation of Urine Chemistry and Sediment<\/a>.<\/i>13<\/sup><\/span><\/p>\n Targeted urine testing includes the urinary corticoid:creatinine ratio (UCCR) and UPC ratio. Testing is minimally invasive and can provide valuable information for screening and diagnosing disease. It may also be used for monitoring disease progression or treatment response. Proper patient selection helps ensure the most useful and cost-effective information.\u00a0<\/span><\/p>\n Cost: <\/b><\/span>$$<\/span><\/p>\n Materials needed:<\/b> Clean container for collecting urine<\/span><\/p>\n UCCR is a valuable screening test that has been used for decades for patients suspected of having hyperadrenocorticism<\/a>.14<\/sup> The test provides an indirect, integrated measure of circulating corticoid production over time by measuring renal excretion of cortisol (free and conjugated). The test therefore eliminates rapid fluctuations in plasma concentrations of cortisol, which can lead to a false-positive diagnosis.15-17<\/sup> This relatively inexpensive test is widely available to clinicians through commercial diagnostic laboratories.18,19<\/sup> The test is used to screen for hyperadrenocorticism in dogs but may also have diagnostic value as a screening test for hypoadrenocorticism<\/a> (sensitivity 97.2% to 100%, specificity 93.6% to 97.3%).14,16,18<\/sup> It should not be used to monitor treatment of hyperadrenocorticism because it is not considered a reliable indicator of successful treatment.20-22<\/sup> The test is advantageous over other screening tests because clients can collect urine from clinically healthy animals in a stress-free home environment. As a screening test for hyperadrenocorticism, UCCR sensitivity is high (75% to 95%), but specificity is poor (reportedly as low as 20%).17,18,23-29<\/sup> The low specificity is attributed to increased corticoid release in stressed healthy dogs (e.g., during hospitalization) and dogs with nonadrenal-associated illness.28,29<\/sup> Therefore, UCCR can help rule out hyperadrenocorticism but should not be used to establish a diagnosis. <\/span><\/p>\n UPC is another valuable urine test that measures the amount of protein loss through the kidneys. It can be valuable for diagnosing and staging disease as well as guiding clinical decisions and treatment response. UPC can also be a prognostic indicator; numerous studies have shown greater risk for death among patients with proteinuria.30<\/sup> This test is recommended for patients with documented proteinuria or suspected proteinuria based on an underlying disease process. The magnitude of UPC elevation can also help identify the location of protein loss (tubular versus glomerular disease).30<\/sup><\/span><\/p>\n Methods and interpretation:<\/b> Because urine collected as a single sample, serial samples, or pooled samples yields similar results, single-sample collection may be preferred due to the ease of collection and analysis.31<\/sup> This diagnostic test is available at reference laboratories and can also be performed in-clinic with some analyzers. UPC should always be performed in <\/span>combination with urinalysis as abnormal urine sediment resulting from disease in the lower urinary tract can also increase the UPC (postrenal proteinuria).30 <\/sup><\/span><\/p>\n Because UPC fluctuates widely day to day, for a single UPC measurement to be considered significant, it must vary substantially. For a safe assumption that proteinuria has increased, single samples must differ by up to 40% in dogs and 90% in cats.30<\/sup><\/span><\/p>\n A UPC of <0.2 is considered to be within normal range, with a UPC of 0.2 to 0.5 in dogs and 0.2 to 0.4\u00a0in cats considered to be borderline proteinuric. To investigate the underlying cause of proteinuria when the UPC is \u22652, additional diagnostics should be performed. UPC ratios of \u22650.5 (dogs) and \u22650.4 (cats) in stable patients should be monitored 2 to 3 times at 2- to 3-week intervals to determine if the proteinuria is progressing. For nonazotemic patients with a UPC \u22652, pathologic glomerular disease should be considered more likely. For patients with chronic kidney disease (i.e., azotemic patients) with UPCs \u22650.5 (dogs) and \u22650.4 (cats), further diagnostics should be performed to elucidate a cause for the proteinuria. When an underlying cause is identified, it should be treated.<\/span><\/p>\n Basal\/resting cortisol testing provides fast, simple, reliable, and cost-effective screening for animals that have clinical signs compatible with hypoadrenocorticism.\u00a0Sensitivity is high (99.4% to 100%) when resting cortisol is <2 \u00b5g\/dL (<55 nmol\/L)32-34<\/sup>; however, specificity is relatively low (63.3% to 78.2%), so it cannot be used as a confirmatory diagnostic test.32,34<\/sup><\/span><\/p>\n Cost: <\/b><\/span>$$<\/span><\/p>\n Materials Needed: <\/b>Serum separator tube<\/span><\/p>\n Interpretation:<\/b> Basal\/resting cortisol testing is better used as a test of exclusion for patients that have waxing and waning unexplained illness, have chronic gastrointestinal signs, or are highly suspected to have hypoadrenocorticism. That is, hypoadrenocorticism should be removed from the differential list for patients with resting cortisol levels of >2 \u00b5g\/dL (>55 nmol\/L). For patients with a resting cortisol of <2 \u00b5g\/dL, an ACTH (adrenocorticotropic hormone) stimulation test should be performed to definitively diagnose hypoadrenocorticism.<\/span><\/p>\n Cost: <\/b><\/span>$<\/span><\/p>\n Materials needed:<\/b> Doppler unit and sphygmomanometer or oscillometric device, appropriately sized blood pressure cuff, ultrasonography gel (<\/span>FIGURE 6<\/b><\/span>).<\/span><\/p>\n Figure 6. Materials needed for noninvasive blood pressure measurement with Doppler technique.<\/p><\/div>\n Indications:<\/b> Systemic arterial pressure is often referred to as the \u201cfourth vital parameter\u201d and provides valuable information about cardiovascular status for anesthetized patients, patients in emergent situations, and patients with associated diseases that pose a risk for the development of hypotension and hypertension. Arterial blood pressure plays a role not only in diagnosis but also in monitoring disease progression and guiding clinicians with therapeutic decision making. <\/span><\/p>\n Methods and interpretation:<\/b> Indirect blood pressure measurement\u00a0involves detecting arterial blood flow or vessel wall movement in a peripheral artery (palmar arterial arches of the forelimb or hindlimb or coccygeal artery of the tail). Oscillometric or Doppler sphygmomanometry techniques provide measurements of systolic arterial blood pressure. <\/span><\/p>\n Indirect blood pressure measurements can vary widely depending on the patient\u2019s signalment and temperament, body condition, measurement technique, and operator experience. Several studies have identified a range of indirect systolic blood pressure measurements of 131 to 151 mm Hg for dogs and 115\u00a0to 162 mm Hg for cats (<\/span>BOX 3<\/b><\/span>).35<\/sup><\/span><\/p>\n Cost of sensor: <\/b><\/span>$$$<\/span> (FreeStyle Libre; Abbott, <\/span>freestylelibre.us<\/span><\/a>)<\/span><\/p>\n Materials: <\/b>Flash glucose monitoring sensor with corresponding applicator and reading device <\/span><\/p>\n Methods and interpretation:<\/b> Historically, glycemic control in patients has been monitored via in-hospital and at-home blood glucose curves, spot blood glucose measurements, urine glucose measurements, and fructosamine measurement.36<\/sup> In recent years, flash glucose monitoring systems (FGMSs<\/a>) have become more popular in veterinary medicine and provide an optimal, low-cost, low-stress way to monitor patients with diabetes. These factory-calibrated devices provide real-time estimates of blood glucose by constantly measuring the glucose concentration of the interstitial fluid through a disc-shaped sensor inserted into the subcutaneous space for up to 14 days. No blood sampling is required for patients with an FGMS; instead, the sensor has to be \u201cflashed\u201d with a portable reader or smartphone at least every 8 hours to retrieve, download, and store glucose measurements (<\/span>FIGURE\u00a07<\/b><\/span>). The data can be uploaded to an online portal for remote interpretation by the clinician. Sensors are easily applied, are well tolerated, and have been validated in dogs and cats.37-41<\/sup><\/span><\/p>\n\n
\n$$ = $50 to $75
\n$$$ = More than $75<\/div><\/div>\nBlood Smear<\/h2>\n
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<\/a><\/a><\/a><\/a><\/p>\n<\/a><\/a>Packed Cell Volume\/Total Protein<\/h2>\n
<\/a><\/p>\n\n
<\/a><\/li>\n<\/a>Urinalysis<\/h2>\n
Physical Characteristics<\/h3>\n
\n
Semiquantitative Chemical Analysis (pH, Blood, Glucose, Ketones, Bilirubin, and Protein)<\/h3>\n
Sediment Evaluation (RBCs, WBCs, Organisms, Epithelial Cells, Crystals, and Casts)<\/h3>\n
Targeted Urine Testing<\/h2>\n
Urinary Corticoid:Creatinine Ratio<\/h3>\n
Urine Protein:Creatinine<\/h3>\n
Basal\/Resting Cortisol<\/h2>\n
Noninvasive Blood Pressure<\/h2>\n
<\/a>\n
Continuous Glucose Monitoring<\/h2>\n