Voided Sample

Voided samples, which are collected as an animal urinates, are the simplest samples to obtain. A sample collected in this manner usually is not satisfactory for bacteriologic examination because the sample is often contaminated during urination. Occasionally, the voided samples have increased numbers of white blood cells (WBCs) and epithelial cells due to contamination from inflammatory lesions of the external genitalia or reproductive tract, but other evaluations are unaffected. A voided sample is collected in a clean, although not necessarily sterile, container. Ideally, the vulva or prepuce should be washed to decrease sample contamination. A midurination (i.e., midstream) sample is best because there is less chance of contamination.

Expressing the Bladder

Urine may be collected from small animals by external, manual compression of the bladder. As with collecting voided samples, the external genitalia should be cleaned before collection. With the animal standing or in lateral recumbency, the bladder is palpated in the caudal abdomen, and urine is expelled by applying gentle, steady pressure. Care must be taken not to exert too much pressure, which could injure or rupture the bladder. This method should never be used on an animal with an obstructed urethra.

Catheterization

Urine may be collected by inserting a catheter of rubber, plastic, or metal into the bladder via the urethra. As in the previous two methods, the external genitalia should be cleaned before the procedure. Sterile catheters are used and sterile gloves worn. Care must be taken to maintain sterility and prevent trauma to the urinary tract. The catheter should pass easily through the urethra. A small amount of sterile, water-soluble lubricating jelly (e.g., K-Y Jelly [Johnson & Johnson Medical Inc, Arlington, Tex.]) should be placed on the tip of the catheter. Because the distal end of many catheters will accept a syringe, urine can be collected with gentle aspiration.

Cystocentesis

Cystocentesis is often used to collect sterile urine samples from dogs and cats. Sometimes as much urine as possible is removed from the bladder to prevent pressure on the bladder wall and urine leakage though the hole created by the needle. Unless the bladder is markedly extended, however, a volume of urine (5 to 10 ml) sufficient to perform urinalysis and culture can be removed without damaging the bladder or causing urine to leak through the bladder wall.

Red Blood Cells

Urine sediment normally contains fewer than 2-3 RBCs/HPF. RBCs are small cells that may have several different appearances, depending on the urine concentration (e.g., specific gravity) and the length of time between collection and examination (Figures 23-4 to 23-9). In fresh samples that have intermediate specific gravities, RBCs usually have smooth edges and are yellow to orange. They can be colorless if their hemoglobin diffused while standing. In concentrated urine, RBCs shrink and crenate (see Figures 23-4 and 23-9). Crenated RBCs have ruffled edges and are slightly darker. Extremely crenated RBCs may even appear granular because of membrane irregularities. In dilute or alkaline urine, RBCs swell and may lyse. Swollen RBCs have smooth edges and are pale yellow or orange. Lysed RBCs may be colorless rings (shadow or ghost cells) that vary in size, but, especially when due to marked alkalinity, they usually dissolve and cannot be identified by microscopic examination.

Figure 23-4 RBCs in urine sediment. All the cells are similar in size, but some have irregular borders because they are crenated because of increased urine osmolarity. (Unstained, original magnification 400×.)

Figure 23-5 Many RBCs in urine sediment. The central dark area in these cells indicates that they have retained their biconcave shape. (Unstained, original magnification 560×.)

Figure 23-6 RBCs and WBCs in urine sediment. The WBCs, which have uncolored cytoplasm, are approximately twice the diameter of the RBCs. (Unstained, original magnification 560×.)

Figure 23-7 In the center of the figure, there are three RBCs and a WBC. The nucleus of the WBC is suggested by the contrast in the center of the cell. (Sedi-Stain, original magnification 560×.)

Figure 23-8 RBCs, a WBC, and two bladder epithelial cells. Note the outline of the nucleus in the more distinct epithelial cell. (Unstained, original magnification 1120×.)

Figure 23-9 A cluster of five bladder epithelial cells and several crenated RBCs. (Unstained, original magnification 1120×.)

RBCs must be differentiated from WBCs in urine sediments. This is easy on stained sediment smears because RBCs are anucleate, but differences in size and internal structure must be used to differentiate between them on unstained smears. RBCs that maintain their biconcave shape can be easily recognized by their dark central area (see Figure 23-5), but those that shrink or swell in response to urine osmolality may not demonstrate the typical biconcave shape. These RBCs are differentiated from WBCs based on size (approximately half the diameter of a WBC; see Figure 23-6) and lack of internal structure. Although RBCs have no nuclei, they should not be confused with fat globules or yeast. RBCs do not vary much in size, are yellow to orange, and tend to settle onto a slide. Fat globules (Figure 23-10) vary markedly in size and are light green and usually found just under the coverslip. (This last feature causes them to be in a different plane of view from other urine sediment elements.) Yeast organisms are rarely found in fresh urine from dogs and cats, but are typically seen in aged samples with overgrowths of contaminants. When present, yeast organisms are more variable in size than RBCs, and budding can usually be found on some of the organisms.

Figure 23-10 There are many fat droplets present in this sample of urine sediment from a cat. The fat droplets are differentiated from RBCs because of the marked variation in size. The fat droplets also settle on a different plain of focus than the cellular elements. (Unstained, original magnification 50×.)

(Courtesy Oklahoma State University, Clinical Pathology Teaching File.)

RBCs in urine usually indicate bleeding somewhere in the urinary or genital tract. Voided samples from females in proestrus, estrus, or postpartum periods often contain RBCs secondary to contamination with secretions from the genital tract. Similar contamination may be present in urine sediments collected by free catch or manual expression of the bladder from animals with any hemorrhagic condition in the genital system. In such cases, RBCs should not be found in urine collected by cystocentesis. Increased numbers of RBCs along with WBCs are usually found in the urine sediment of animals with inflammatory conditions of the urinary tract. The slight trauma that occurs from catheterization or manual expression, and occasionally with cystocentesis, can increase the number of RBCs in the sediment.

White Blood Cells

Very few WBCs are present in urine from animals without urinary or genital tract disease. WBCs are about twice the size of RBCs and smaller than epithelial cells (see Figures 23-6 to 23-8). They are round and granular and sometimes brownian movement of the cytoplasmic granules in the neutrophils is seen. The polymorphic neutrophil nuclei can usually be seen in stained sediments and with phase-contrast microscopy and may occasionally be seen with reduced illumination bright field microscopy. WBCs are usually in very low numbers in urine (i.e., 0 to 1/HPF); more than 2 to 3 WBCs/HPF indicates inflammation somewhere in the urinary or genital tract. When increased numbers of neutrophils are found in urine sediment, even if bacteria are not found by microscopic examination, the urine sample should be cultured because microscopic examination is much less sensitive than culture to detecting bacteria in urine.

Epithelial Cells

Epithelial cells in urine vary markedly in size depending upon their origin. They are generally larger in the lower portions of the urinary tract than in the ureters, renal pelvis, and renal tubules.

Squamous Epithelial Cells

Squamous epithelial cells, which are derived from the distal urethra, vagina, vulva, or prepuce, are occasionally found in voided samples (Figure 23-11) and are usually not considered significant. They are the largest of the epithelial cells and the largest cells found in urine sediment; they appear flat and often have straight edges and obtuse, angular corners. They usually have a small, round nucleus, although occasionally a nucleus cannot be seen. Squamous epithelial cells are usually not found in samples obtained by cystocentesis. Cells with squamous features can be found in the urine sediment of male dogs with conditions that cause squamous metaplasia of the prostate and occasionally in the sediment of those with urothelial carcinomas (i.e., transitional cell carcinomas) in which there is also squamous metaplasia. In the latter condition, many other features suggestive of epithelial neoplasia, including extreme numbers of epithelial cells with marked pleomorphism, are found.

Figure 23-11 A, A squamous epithelial cell from the distal urethra as seen with reduced illumination and bright field microscopy. B, The same cell seen with phase-contrast microscopy. (Unstained, original magnification of both figures 880×.)

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