Pyuria
Pyuria is defined as gross or microscopic evidence of inflammatory cells in the urine. Dysuria, stranguria, pollakiuria, crystalluria, urine scalding, and hematuria can accompany it.
Pyuria may result from systemic septic inflammatory disease, localized microbial UTI, or nonseptic inflammation (sterile pyuria; see Fig. 10.2). In horses, the normal variable turbidity of equine urine should be considered when assessing gross pyuria. Causes of pyuria are listed in Box 10.3.Approach to Diagnosis of Pyuria
A complete examination of the urinary tract should be performed, including rectal palpation or transabdominal palpation of the bladder. Cystitis may be characterized by a thickened bladder wall, but this is often difficult to detect during rectal palpation and ultrasonographic examination may be necessary. Predisposing factors for UTI such as urinary calculi, dystocia, abnormal urethral or genital structure, and neurologic diseases should always be considered.
■ BOX 10.3
Causes of Pyuria in Horses and Ruminants
Admixture of inflammatory exudate from the reproductive tract (spurious pyuria)
Calculi (uroliths, nephroliths)
Ectopic ureter
Encircling hair rings of the penis
Infection of the urinary tract (urethritis, cystitis, ureteritis, and/ or pyelonephritis), including Leptospirosis
Neoplasia
Nephritis (sterile)
Penile, preputial, or urethral trauma
Rectovaginal fistula
Ulcerative posthitis (small ruminants) and vulvovaginitis Viral infections of the genitalia
Vulvar, vaginal, or urethral trauma or neoplasia
Pyuria is confirmed by obtaining a midstream (free catch) or catheterized urine sample and by quantitating the number of white blood cells (WBCs) and bacteria in the urine sediment. Evaluation of urine sediment within 30 to 60 minutes of collection enables preservation of the greatest cytologic detail.
In human medicine, pyuria is defined as the presence of more than 10 WBCs per mm3 urine, 3 or more WBCs per microscopic high-power field (HPF) or positive Gram staining on unspun urine, or leukocyte esterase positive on a urinary dipstick.12 In horses, to the authors' knowledge, no peer-reviewed study has specifically assessed the cellular content of urine in healthy horses. Pyuria is generally considered to be the presence of more than 10 WBCs per HPF of a midstream-voided or catheterized sample, and the urine of normal horses and cattle generally is said to have fewer than 5 WBCs per HPF.13,14 However, a study assessing quantitative cultures in free catch urine from healthy horses found that no horse had a WBC count of more than 1 per HPF.15 This suggests that the generally accepted number of more than 10 WBCs per HPF to diagnose pyuria may be too high for horses and that pyuria should be suspected if more than 5 WBCs per HPF are seen, providing collection is aseptic and there is clinical suspicion. When bacterial infection is the cause of pyuria, there are typically more than 20 organisms visible per HPF. The cytologic features of urine sediment and quantitative culture are influenced by the method of collection, rigor of aseptic technique, and degree of contamination of the prepuce, vulva, and urethral orifice. Catheterization can be used to obtain urine from the bladder of most male and female horses and female ruminants. If adequate quantity is obtained, the first 20 mL collected should be discarded and analysis done on the subsequent 20 mL.15 In male ruminants, the urethral recess (diverticulum) prevents retrograde catheterization of the bladder, and collection of a midstream sample is usually the sole option. Cystocentesis of a large animal with a UTI carries the risk of induction of septic peritonitis.Urine samples should be refrigerated and quantitative culture performed as soon after collection as possible to avoid false increases in the colony count that can occur from bacterial proliferation in the sample during storage.
The results of quantitative culture are greatly influenced by the method of collection and the degree of contamination of the prepuce and vulva. In specimens collected by midstream free catch, bacterial counts greater than 1 ? 104 bacteria/mL of urine are indicative of UTI if compatible dipstick and sediment examination findings are present. Normal equine urine has fewer than 20,000 colony-forming units (CFUs)/mL in a free catch sample and fewer than 500 CFUs/mL in a catheterized sample.15 In free catch urine samples from horses, mean CFU/mL bacterial counts are significantly higher in females (6054 CFU/mL) than in males (490 CFU/mL).15 A culture that yields a large number of a variety of bacterial species may reflect heavy contamination of the vulva or penis, fecal admixture, a UTI involving multiple bacterial species (rare), or delay before culture was initiated, especially if the urine sample was not kept refrigerated.Once pyuria is confirmed, its location or origin, inciting cause(s), and any predisposing conditions should be determined. In males, the accessory sex glands should be carefully examined because inflammatory exudate from these structures may be admixed with urine, resulting in a spurious diagnosis of pyuria. In females, mixing of urine and inflammatory exudate in the urethra and vestibule may also result in spurious pyuria. Trauma or inflammation of the glans penis or prepuce can also result in admixture of exudate with urine, as often occurs in ulcerative posthitis in rams and bucks. Endoscopic examination of the vaginal vault or preputial cavity may be helpful, using air insufflation to aid in visualization of the mucosa. Inflammatory diseases of the LUT usually produce obvious clinical signs of dysuria but minimal to no signs of systemic disease. Low-grade fever is occasionally present in cases of localized cystitis, although affected animals are often not apparently systemically ill.
If the pyuria originates from the UUT, the animal is usually persistently or intermittently febrile and shows systemic signs of disease, and changes suggestive of inflammation are often present on a CBC.
Inflammation of the ureter(s) and kidney(s) may result in colic. Rectal examination may reveal enlargement of one or both ureters, pain on palpation, and possibly enlargement and/ or abnormal shape of the left kidney. If grossly enlarged, the right kidney can occasionally be palpated per rectum in horses or cattle. In cows and heifers, thickening and pain of one or both ureters is often more readily identified during vaginal palpation than rectal palpation. Casts of blood, protein, or cellular debris may be seen in the urine sediment in cases of pyelonephritis. An ultrasonographic examination of both kidneys and ureters should be performed in all animals with evidence of upper UTI. The technique for ultrasound examination of the urinary tract is described in Equine Abdominal Ultrasonography and Ruminant Abdominal Ultrasonography in Chapter 32.If Leptospira interrogans serotype Pomona is suspected as a cause of pyuria (cattle), urine sediment should be placed on a microscope slide, air-dried, and examined by fluorescent antibody for Leptospira antigen.16 Polymerase chain reaction testing for Leptospira species can be performed on urine sediment in cattle, goats, and horses; in cattle, greater sensitivity may be achieved by obtaining a urine sample after administration of furosemide.17 19