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Basics ⬇

Basics

Definition

  • WBCs (i.e., neutrophils, eosinophils, monocytes, lymphocytes, or plasma cells) in urine.
  • More than 5 WBCs per high-power field is generally considered abnormal, but the number of WBCs found in urinary sediment varies with method of collection, sample volume and concentration, degree of cellular destruction after collection, and laboratory technique.

Pathophysiology

  • Large numbers of WBCs in voided urine samples indicate active inflammation somewhere along the urogenital tract.
  • Can be associated with any pathologic process (infectious or non-infectious) that causes cellular injury or death; tissue damage evokes exudative inflammation characterized by evidence of leukocytic extravasation (pyuria) and increased vascular permeability (hematuria and proteinuria).

Systems Affected

  • Renal/Urologic-urethra, urinary bladder, ureters, and kidneys
  • Genital-prepuce, prostate, vagina, and uterus

Signalment

Dog and cat

Signs

General Comments

  • Inflammation can cause clinical signs localized to the site(s) of injury or may be accompanied by systemic manifestations. Historical and physical examination findings depend on the underlying cause, organ(s) affected, degree of organ dysfunction, and magnitude of systemic inflammatory responses.
  • Non-obstructive lesions confined to the urinary bladder, urethra, vagina, or prepuce rarely cause systemic signs of inflammation. Systemic signs may accompany generalized inflammatory lesions of the kidneys, prostate, or uterus.

Physical Examination Findings

Local Effects of Inflammation

  • Erythema of mucosal surfaces-e.g., redness of vaginal or preputial mucosa
  • Tissue swelling-e.g., renomegaly, prostatomegaly, mural thickening of urinary bladder or urethra
  • Exudation of leukocytes and protein-rich fluid-e.g., pyuria, purulent urethral or vaginal discharge, pyometra, or prostatic abscess
  • Pain-e.g., adverse response to palpation, dysuria, pollakiuria, stranguria
  • Loss of function-e.g., polyuria, dysuria, pollakiuria, urinary incontinence

Systemic Effects of Inflammation

  • Fever
  • Depression
  • Anorexia
  • Dehydration

Causes

Kidney

  • Pyelonephritis-e.g., bacterial, fungal, parasitic, or mycoplasmal
  • Nephrolith(s)
  • Neoplasia
  • Trauma
  • Immune-mediated

Ureter

  • Ureteritis-e.g., bacterial
  • Ureterolith(s)
  • Neoplasia

Urinary Bladder

  • Cystitis-e.g., bacterial, mycoplasmal, fungal, or parasitic
  • Urocystolith(s)
  • Neoplasia
  • Trauma
  • Overdistension-urethral obstruction
  • Pharmacologic-cyclophosphamide

Urethra

  • Urethritis-e.g., bacterial, fungal, or mycoplasmal
  • Urethrolith(s)
  • Neoplasia
  • Trauma
  • Foreign body

Prostate

  • Prostatitis/abscess-e.g., bacterial or fungal
  • Neoplasia

Penis/Prepuce

  • Balanoposthitis
  • Neoplasia
  • Foreign body

Uterus

Pyometra/metritis-e.g., bacterial

Vagina

  • Vaginitis-bacterial, mycoplasmal, viral, or fungal
  • Neoplasia
  • Foreign body
  • Trauma

Risk Factors

  • Any disease process, diagnostic procedure, or therapy that alters normal host urinary tract defenses and predisposes to infection.
  • Any disease process, dietary factor, or therapy that predisposes to formation of metabolic uroliths.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

Voided Specimens

  • Rule out vaginitis-signs include vaginal discharge, erythema of vaginal mucosa, licking of vulva, and attracting male dogs.
  • Rule out pyometra, metritis-signs include vaginal discharge, large uterus, pyrexia, depression, anorexia, polyuria, polydipsia, and a recent history of estrus, parturition, or progestin administration.
  • Rule out balanoposthitis-signs include preputial discharge, erythema of preputial or penile mucosa, and licking of prepuce.
  • Rule out prostatitis, prostatic abscess, or prostatic neoplasia-signs include urethral discharge, prostatomegaly, pyrexia, depression, dysuria, tenesmus, caudal abdominal pain, and stiff gait.
  • Rule out urethritis, urethroliths, urethral neoplasms-signs include dysuria, pollakiuria, stranguria, and/or palpable uroliths or mass lesions in the urethra.
  • Rule out inflammatory disorders of urinary bladder and kidneys.

Specimens Collected by Cystocentesis

  • Rule out urethral obstruction-signs include stranguria, anuria, and a large overdistended urinary bladder.
  • Rule out prostatic and urethral disorders (see above); purulent prostatic or urethral exudates can reflux into the urinary bladder.
  • Rule out cystitis, urocystoliths, and urinary bladder neoplasia-signs may include dysuria, pollakiuria, stranguria, and/or palpable uroliths or mass lesions in the urinary bladder.
  • Rule out pyelonephritis-signs may include pyrexia, depression, anorexia, polyuria, polydipsia, renal pain, and renomegaly.
  • Rule out post-traumatic pyuria-signs may include history of trauma, including iatrogenic causes.

Laboratory Findings

Drugs That May Alter Laboratory Results

  • WBCs lyse rapidly in hypotonic or alkaline urine. Administration of alkalinizing agents (e.g., sodium bicarbonate, potassium citrate, chlorothiazide, or acetazolamide) or agents that produce hypotonic urine (e.g., diuretics and glucocorticoids) may falsely decrease urine WBC numbers.
  • Leukocyte esterase reagent strip (dipstick) methods are not recommended for use in canine (not sensitive) or feline (not specific) urine samples. In addition, nitrofurantoin, cephalosporins, and gentamicin can cause false-positive leukocyte esterase reactions.
  • Urinary WBC concentrations can be low in patients with inflammatory disorders who have been given steroidal or nonsteroidal anti-inflammatory drugs.

Disorders That May Alter Laboratory Results

  • Disorders associated with diminished WBC function or absolute neutropenia can artificially lower WBC values.
  • Disorders associated with production of hypotonic urine or alkaline urine artificially lower WBC values.

Miscellaneous Factors That May Alter Laboratory Results

  • False-negative leukocyte esterase reaction in dogs when urine is tested by the reagent strip (dipstick) method.
  • False-positive and false-negative leukocyte esterase reaction in cats when urine is tested by the reagent strip (dipstick) method.

Valid if Run in Human Laboratory?

Valid if urinary sediment is examined microscopically; invalid if only leukocyte esterase reagent strip (dipstick) method is used.

CBC/Biochemistry/Urinalysis

  • Pyuria in specimens collected by voiding, manual compression, or transurethral catheterization indicates an inflammatory lesion involving at least the urinary or genital tracts.
  • Pyuria in specimens collected by cystocentesis localizes the site of inflammation to at least the urinary tract, but does not exclude the urethra and genital tract. Reflux of prostatic exudates into the urinary bladder may result in pyuria in patients with prostatic disease.
  • Pyuria associated with WBC casts is unequivocal evidence of renal parenchymal inflammation.
  • Generalized renal injury may be associated with concomitant leukocytosis, isosthenuria, and azotemia.
  • Pyuria associated with bacteria, fungi, or parasite ova in sufficient numbers to be seen by microscopic sediment examination indicates that the inflammatory lesion was caused or complicated by urinary tract infection. Detection of bacteria in urine sediment by light microscopy may be enhanced by placing a drop (20 µL) of urine sediment on a glass slide, allowing it to dry without spreading, staining with Diff-Quik and examining for bacteria under oil immersion (1,000 ×).
  • Pyuria associated with neoplastic cells indicates neoplasia. Diagnosis of urinary tract neoplasia by cytologic examination of urine may be complicated by epithelial cell hyperplasia and atypia caused by urinary tract inflammation or the physiochemical properties of urine (pH and tonicity causing cell scalding).

Other Laboratory Tests

  • Perform quantitative urine culture on all patients with pyuria; it provides the most definitive means of identifying and characterizing bacterial urinary tract infection. It is important to note that the absence of pyuria does not rule out the bacteriuria as patients with bacteriuria frequently do not have pyuria.
  • Negative urine culture results suggest a non-infectious cause of inflammation (e.g., uroliths, neoplasia) or inflammation associated with urinary tract infection caused by fastidious organisms (e.g., mycoplasmas and viruses) or by organisms capable of forming intracellular bacterial colonies or biofilms. False-negative culture results may also be due to recent antimicrobic therapy, sample mishandling, or delays between specimen collection and culture.
  • Cytologic evaluation of urinary sediment, prostatic fluid, urethral or vaginal discharges, or biopsy specimens obtained by catheter or needle biopsy may help evaluate patients with localized urinary or genital tract disease. Cytologic examination may establish a definitive diagnosis of urinary tract neoplasia, but negative cytologic findings do not rule out neoplasia.

Imaging

Survey abdominal radiography, contrast urethrocystography and cystography, urinary tract ultrasonography, and excretory urography are important means of identifying and localizing underlying causes.

Diagnostic Procedures

  • Urethrocystoscopy-indicated in patients with persistent lesions of the lower urinary tract for which a definitive diagnosis has not been established by other, less invasive, means.
  • Light microscopic evaluation of tissue specimens-indicated in patients with lesions of the urinary or genital tracts for which a definitive diagnosis has not been established by other, less invasive, means; tissue specimens may be obtained by membrane disruption (traumatic) catheterization biopsy, cystoscopy and forceps biopsy, or exploratory laparotomy; aspiration and punch biopsy techniques may be used to evaluate the prostate gland.

Treatment ⬆ ⬇

Treatment

Medications ⬆ ⬇

Medications

Drug(s)

Depend on underlying cause

Contraindications

  • Avoid glucocorticoids or other immunosuppressive agents in patients suspected of having urinary or genital tract infection.
  • Avoid potentially nephrotoxic drugs (e.g., gentamicin) in febrile, dehydrated, or azotemic patients and those suspected of having pyelonephritis, septicemia, or pre-existing renal disease.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

Response to treatment by serial urinalyses, including examination of urine sediment; collect specimens from most patients by cystocentesis to avoid contamination by preputial or vaginal exudates; perform transurethral catheterization if the expected benefits outweigh the risk of iatrogenic bacterial urinary tract infection.

Possible Complications

  • Infectious and non-infectious inflammatory disorders of the urinary tract can cause primary renal failure, urinary obstruction, uremia, septicemia, and death.
  • Pyuria is a potential risk factor for formation of matrix or matrix-crystalline urethral plugs and subsequent urethral obstruction in male cats.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

  • Hematuria
  • Proteinuria
  • Bacteriuria

Synonyms

Leukocyturia

See Also

Abbreviation

WBC = white blood cell

Suggested Reading

Adams LG, Syme HM. Canine ureteral and lower urinary tract diseases. In: Ettinger SJ, Feldman EC, eds., Textbook of Veterinary Internal Medicine, 7th ed. St. Louis: Elsevier, 2010, pp. 2086–2115.

Forrester SD, Kruger JM, Allen TA. Feline lower urinary tract diseases. In: Hand MS, Thatcher CD, Remillard RL, et al, eds. Small Animal Clinical Nutrition, 5thed. Topeka: Mark Morris Institute, 2010, pp. 925–976.

Francey T. Prostatic Diseases. In: Ettinger SJ, Feldman EC, eds., Textbook of Veterinary Internal Medicine, 7th ed. St. Louis: Elsevier, 2010, pp. 2047–2058.

Pressler B, Bartges JW. Urinary tract infections. In: Ettinger SJ, Feldman EC, eds., Textbook of Veterinary Internal Medicine, 7th ed. St. Louis: Elsevier, 2010, pp. 2036–2047.

Osborne CA, Stevens JB, Lulich JP, et al. A clinician's analysis of urinalysis. In: Osborne CA, Finco DR, eds., Canine and Feline Nephrology and Urology, 2nd ed. Baltimore: Williams & Wilkins, 1995, pp. 136–205.

Phillips J. Neoplasia of the lower urinary tract. In: Bartges J, Polzin DJ eds. Nephrology and Urology of Small Animals. Chichester, UK: Wiley-Blackwell, 2011, pp. 797–808.

Authors John M. Kruger, Carl A. Osborne, and Cheryl L. Swenson

Consulting Editor Carl A. Osborne