American Society for Veterinary Clinical Pathology
2424 American Lane
Madison, WI 53704

Telephone: +1-608-443-2479
Fax: +1-608-443-2474
email: info@asvcp.org

 

2.5. Urinalysis

 

2.5.1. Monitoring – see General recommendations

2.5.2. Method Validation – see General recommendations.  Not all of the method validation experiments listed in section 2.1.2. may be applicable to evaluation of urinalysis.  Method validation experiments should be selected or modified as necessary to ensure that new methods/analyzers are functioning satisfactorily to meet the laboratory's requirements and the manufacturer's specifications. Applicable method validation procedures may include, but are not limited to, comparison of methods, testing for interference (particularly how urine color effects ability to read strip result visually or by automated methods), and possibly detection limits.

2.5.3. Instrumentation - see General Recommendations. Instrumentation employed in urinalysis is limited but may include automated strip readers.  Automated strip reader should be maintained and operated according to manufacturer's specifications.  Applicable function checks should be done as needed to ensure accurate instrument performance.

2.5.4. Personnel Knowledge. 

a. Understanding of the effects of specimen condition on test parameters, e.g., effect of hemoglobinuria on protein determination.

b. Knowledge of species-specific crystalluria and expected findings.

c. Knowledge of common problems encountered with veterinary urine specimens that may lead to erroneous results, e.g., effects of preservatives on test results, urine specimen incorrectly run on serum settings

d. Knowledge of dip-stick methodology used in the laboratory and common interferences for that method.

e. Appropriate uses of retest criteria:  Established by laboratory and based on clinical significance of test values, e.g., crystal identification, protein confirmation by semi- or analytic quantitation, glucose confirmation. Tablets methods may be required when intensely pigmented urine interferes with ability to read the dip-stick pads.  Include documentation of retesting on worksheet and report or corrected reports (if necessary).

2.5.5. Quality Control – see also General recommendations

a. Assays

i. Physical Tests (appearance [color, clarity], specific gravity [estimation by refractometry])

ii. Chemical Tests

1. 'Dipstick' tests

2. Confirmatory tests (glucose [tablet], bilirubin [tablet], ketones [powder or tablet], sulfosalicylic acid precipitation for protein)

b. Quality control procedures for dipstick and urine specific gravity.  Urinalysis control materials for human urine are available for testing accuracy of dipsticks.  Frequency of QC testing of dipsticks depends on the number of procedures performed by the laboratory and may vary from daily QC testing to QC testing with each newly opened bottle of dipsticks.  Accuracy of refractometers should be monitoring at regular intervals using distilled water (SG 1.000).(George, 2001)

c. Microscopic examination of sediment: standardization of procedure

i. Microscopic sediment examination of veterinary urine specimens requires training. Texts, charts and posters of formed elements in urine for a variety of species should be accessible to the analyst.   The details of performing this task and the results to be reported may be outlined or detailed in a laboratory SOP.

ii. A standard volume of urine is used for preparing urine sediment (e.g., 5 or 10 mL), depending upon the species and the tests requested.  Conical centrifugation tubes should be spun at low RPM, e.g., 400-500g for 5 minutes.  High RCF and excessive centrifugation time destroys casts and cellular elements. RCF = 1.118x10-5 x radius of arm(cm) x revolutions/min.

iii. Supernatant is removed by decanting or pipetting, so that a constant volume of supernatant remains with the pellet (preferred volume 0.5 mL).  Cellular elements are then resuspended by gentle mixing.

iv. Stain may be added to resuspended sediment to facilitate identification of sediment contents.  A consistent number of drops should be added followed by gentle mixing.  Additional dilution of cellular elements caused by volume of stain should be factored into final results. Alternatively, a constant sediment volume can be maintained by replacing some of the supernatant volume with stain.

v. A pipette is used to transfer one or two drops of sediment to a glass slide, depending upon the coverslip dimensions.  It is important that the sediment volume, the number of drops of sediment and the coverslip size used are constant within a laboratory.

vi. Alternative methods of standardization of urine sediment are available (e.g., volumetric counting grids, automated methods), but are not frequently used in veterinary medicine.  Adoption of any new methodology should be preceded by method validation studies.  

d. Microscopic examination of sediment: enumeration of elements

i. The sediment contents are examined at low magnification (x100 or LPF) followed by high-dry magnification (x400 or HPF) and rarely oil immersion magnification (x1000 or oil).  Several formats have been used for reporting grades and amounts of the formed elements.  Absolute numbers have many advantages.  The low and high amounts of each element observed in 10 fields, or the average, are reported. Alternatively, a 0 to 3+, or 0 to 4+, grading system may be used, if clear criteria are written for technologists to use.  This information also should be provided to clinicians or customers.  The urine sediment SOP should clearly describe procedures for examining and reporting sediment contents.

ii. Low power field (LPF) is used for enumeration of casts.  Casts are reported by type and number per LPF.  LPF also can be used for general assessment of the distribution of crystals, epithelial cells and background contents (mucus, sperm, fat, yeast, etc.). 

iii. High power field (HPF) is used for reporting numbers of erythrocytes, leukocytes, and possibly crystals, epithelial cells, and bacteria when in high numbers.

iv. Oil magnification may be used for reporting concentration and morphology of bacteria or other cellular elements.

v. Observation of microorganisms (e.g., bacterial rods or cocci, yeast) in unstained or stained wet mounts should be confirmed with a quick stain or Gram stain on an air-dried slide made from straight or concentrated urine of the sediment.   

 

2.5.6. Procedures Manual – see General recommendation

2.5.7. Comparison of Tests- see General recommendations

2.5.8. Identification of out-sourced tests – see General recommendations