Today's Veterinary Practice

MAY-JUN 2014

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Today's Veterinary Practice May/June 2014 90 | Today's Technician tvpjournal.com spiculated and small due to d e h y d r a t i o n , and lyse in urine that is not ana- lyzed quick ly. Lysis is acceler- ated in either d i lut e u r i ne (USG < 1.006) or alkaline urine, which results in a positive occult blood reading on the dipstick, but no visible erythrocytes on sed- iment examination. This result may be misdiagnosed as hemoglobinuria associated with intravascular hemolysis. White Blood Cells. Up to 5 white blood cells (WBCs) per HPF may be present in healthy animals. WBCs are round, approximately 1½ to 2 times the size of RBCs, and have refractive internal granularity that is more pronounced with fine focusing manipulation. WBCs in urine are typically neutrophils. Pyuria describes the presence of 6 to 10 or more neutrophils per HPF (Table 3). Unstained wet mount preparations present 2 challeng- es: (1) leukocytes may be present but cannot be readily differentiated and (2) it may be difficult to differentiate WBCs from small epithelial cells. WBCs deteriorate in urine and may decline up to 50% within an hour of collection if the sample is kept at room temperature. 3 Epithelial Cells. Low numbers of epithelial cells are found in the urine of healthy animals; particularly those samples obtained by catheterization, as cells slough and are replaced by new cells. In unstained wet mounts, it is difficult to differentiate epithelial cells based on size. • Renal tubule cells are typically small, but distinguish- ing them from WBCs or small transitional cells may not be possible. Increased numbers of small epithelial cells should prompt evaluation of an air-dried, stained cytology preparation to distinguish WBCs and/or tran- sitional cells from renal tubule cells. Sloughing of renal tubule cells indicates renal tubule damage. • Transitional cells (Figure 7, page 89) line the renal pel- vis, ureters, urinary bladder, and most of the urethra. They vary greatly in size, but are typically 2 to 4 times larger than WBCs, with a round nucleus and granular cytoplasm. Increased numbers of transitional cells may be seen with inflammation of the urinary bladder. This finding should prompt cytologic examination of an air- dried, stained sample to evaluate the cells for evidence of malignancy. • Squamous cells (Figure 8, page 89) are located at the distal urethra and genital tract of females. They are large, polygonal cells considered contaminants. Casts Urinary casts are cylindrical molds formed in the lumens of the renal tubules. They are primarily composed of a mucoprotein secreted by renal tubule cells. Concentrat- ed urine, decreased urine flow, and acidic urine favor the formation of casts. Cells and other material (lipid, crystals) may be integrat- ed into casts, changing their appearance and how they are characterized (Table 4). • Hyaline casts are clear, composed only of mucoprotein (Figure 9). They deteriorate in alkaline urine. • Cellular casts (erythrocytes, leukocytes, renal tubule cells, lipid) form as the cellular component becomes incorporated into the mucoprotein matrix in the lumen of the tubule (Figure 10). Progressive degradation of cel- lular casts leads to the characterization of coarsely granu- lar, finely granular, and finely waxy casts (Figure 11). • Casts may be pigmented by bilirubin, hemoglobin, or myoglobin. 1 Less than 2 per LPF hyaline and > 1 per LPF granu- lar casts may be found in urine from healthy animals. 1,3 Increased numbers of casts in the urine (cylinduria) local- izes a disease process to the kidneys. Crystals Crystals are commonly found in urine. Their formation is dependent on oversaturation of the mineral substrate and urine pH. Crystals may be associated with urolithiasis or other medical condition or have no diagnostic significance. • Struvite crystals may be observed in neutral to alkaline urine of dogs and cats. These crystals can form in vitro in stored, uncovered urine (Figure 12). • Calcium oxalate dihydrate (weddellite) crystals may be observed in healthy animals (Figure 13). They may also be present with calcium oxalate monohydrate (whewellite) crystals—which are not found in healthy animals (Figure 14), but in patients with ethylene gly- col poisoning. Figure 9. Hyaline cast Figure 10. Fatty cast; lipid droplets in background Figure 11. Granular cast TabLe 3. causes of Pyuria • contamination from the prepuce or vagina/vestibule • Genital tract inflammation • inflamed neoplasia • Urinary tract infection • Urinary tract inflammation TVP_2014-0506_TT_Urinalysis-Part2.indd 90 5/25/2014 7:28:48 PM

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