Felis ISSN 2398-2950

Urinalysis: overview

Contributor(s): Melissa Wallace, SYNLAB-VPG

Overview

  • Changes in the chemical and physical characteristics of urine occur in many diseases, eg urogenital disease, hepatic disease, hematological disorders, endocrinopathies, neoplasia and musculoskeletal disease.
  • Changes in these characteristics can aid in the diagnosis of many diseases in ill animals and act as a cost-effective screening test in asymptomatic animals, or for monitoring specific disease changes and therapeutic response.

Sampling

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Tests

Methodologies

Physical appearance

  • Color: to check for possible interference and abnormal (non yellow) colors (eg red-blood).
  • Turbidity: macroscopic parameter which results from noted sediment findings (eg lipid droplets in iatrogenic samples).

Chemical analysis

  • Warm refrigerated sample to room temperature as the USG and enzymatic tests are all temperature dependent.
  • Centrifuge a set volume (minimum 0.5 ml) at slow speed for 10 mins (eg 500g, see conversion formula for rpm).
  • Decant supernatant for chemical analysis and USG, leaving sediment for microscopy (eg 1 drop following 0.5 ml centrifugation).
  • Determine specific gravity (USG) Urinalysis: specific gravity by refractometer on the supernatant.
  • Dipstick specific gravity pads do not correlate well with refractometry and should not be used. Veterinary specific refractometers are ideal which have a specific cat reference scale too. Otherwise the standard (human) scale can be converted using the formula:
    • Feline SG = (0.846 x reading) + 0.154
  • Perform dipstick analysis Urinalysis: dipstick on the supernatant, comparing the color change of dipstick to the reference range at the correct time of reading (often 1 min / 60 s). The color change is typically enzymatic so time and temperature dependent too.
  • Rapidly and completely immerse the dipstick and then tip sideways to blot off excess and prevent cross-reaction between the pads. Alternatively if a small volume, use a pasteur pipette to streak or pipette urine drops onto each pad, before tipping off the excess.

Microscopic examination

  • Leave 0.25 ml urine in the Eppendorf or centrifuge tube.
    • Resuspend the sediment by repeatedly flicking or ‘racking’ the centrifuge tube. Repeated (5 times) gently withdrawing and expressing via the pipette can also be used.
    • Using a fine tip pasteur pipette, once evenly resuspended, transfer one drop of sediment to a microscope slide and place a coverslip (18 x 18mm typically) over it.
    • Lower the substage condenser on the microscope to maximise the diffraction.
    • Systematically examine the entire specimen under the lower power objective (x10-20) initially to check and semi-quantify (occ., +, ++, +++) for large epithelial cells, casts and crystals.
    • Examine the sediment under the high power objective (hpf, x40) to confirm the morphology of certain elements (eg small calcium oxalate crystals) and to detect bacteria.  Average the number of red and white cells per hpf by counting at least 5 fields of view.
  • 1 drop of Sedistain TM or a supravital stain such as Sternheimer-Malbin Staining techniques: Sternheimer-Malbin can be added to the standard sediment volume to highlight some cell features, notably nuclei for WBC identification. It does though obscure crystal colours.
  • However, stain deposits or precipitates and bacterial contaminant growth in the reused bottle and its pipettor, as well as varying the number of drops used, all lead to misleading results and mis-diagnosis, such as confusing precipitate as bacteria to mis-diagnose a UTI.

Availability

  • Can be performed in-house by veterinary clinics with an SOP and appropriate training.
  • Access to variable speed centrifugation quickens the analysis but is not essential.
  • All external laboratories but potentially greater in vitro change.

Technician (extrinsic) limitations

  • A standard operating procedure (SOP) should always be used on a designated plain and standardised volume of urine to provide accurate, reproducible and consistent results. This allows disease changes and therapy to be monitored over time accurately, no matter who performs the testing. Experience adds to the familiarity and speed over time.

Result Data

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Further Reading

Publications

Refereed Papers

  • Recent references from VetMed Resource and PubMed.
  • Ling G V, Norris C R, Franti C E, Eisele P H, Johnson D L, Ruby A L & Jang S S (2001) Interrelations of Organism Prevalence, Specimen Collection Method, and Host Age, Sex and Breed among 8,354 Canine Urinary Tract Infections (1969-1995). JVIM 15(4), 341-347 PubMed.

Other sources of information

  • Osbourne C A et al (1999) Urinalysis: A Clinical Guide to Compassionate Patient Care. Bayer.


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