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Urinalysis: a step by step approach (Proceedings)


Collection

Always record the method of collection as it is important in interpretation of results

Midstream catch (voided sample)

  • Advantages: no risk to the patient and owners can collect it.
  • Disadvantages: contamination with cells, bacteria, and other debris located in the genital tract, or on the skin and hair, and the patient doesn't always cooperate.

Manual expression
  • Advantages: little risk and ability to collect urine at your convenience as long as there is a full bladder.
  • Disadvantages: bladder may not have enough urine or may be difficult to express, possible to traumatize the bladder and cause hematuria, urine is frequently contaminated with cells, bacteria, and other debris located in the genital tract, or on the skin and hair

Catheterization

  • Advantages: can collect urine at your convenience and decreases contamination from skin, hair, and genital tract.
  • Disadvantages: potential for trauma and hematuria and potential for introducing bacteria into the bladder from the urethra

Cystocentesis

  • Advantages: often better tolerated than catheterization, decreased risk of iatrogenic urinary tract infection, prevents contamination of the urine by cells, debris, and bacteria from the lower urogenital tract, and aids in the localization of hematuria, pyuria, or bacteriuria.
  • Disadvantages: need adequate urine within the bladder, potential for trauma, and is frequently contaminated with blood.

Handling

Perform urinalysis within 30 minutes of collection or refrigerate. Allow urine to warm up to room temperature before analysis if it has been refrigerated.

A complete urinalysis includes the following:

  • Gross observation
  • Measurement of solute concentration (specific gravity)
  • Measurement of chemical constituents and pH (typically with a dipstick)
  • Sedimentation and microscopic evaluation

Gross observation:

Color

  • Can be colorless to dark yellow depending on concentration
  • Dark yellow to brown may be due to bilirubin
  • Red
  • Erythrocytes (hematuria)
  • Hemoglobin (red to red-brown)
  • Myoglobin (reddish brown)

Turbidity / Transparency

  • Most species – clear
  • Horses – cloudy (calcium carbonate crystals and mucous)
  • Cloudiness indicates presence of formed elements
  • Microscopic exam should always be used to determine the cause (crystals, cells, mucus, casts, bacteria, spermatozoa). If urine is not evaluated when fresh, crystals may have formed, causing cloudiness

Urine specific gravity (USG)

  • Specific gravity is influenced by the number of solute molecules plus molecular size and weight. It's an estimate of the kidney's ability to concentrate or dilute urine.
  • Place one drop of urine on the refractometer and read the value directly from the specific gravity scale.