Urinalysis

The routine urinalysis is a quick and relatively inexpensive test which can be readily performed in a field laboratory. Ideally urine should always be collected at the same time as blood for hematology and clinical chemistry (if possible) and before any treatment is administered.

Urine should be examined as soon as possible after collection, because artifacts will occur in the urine over time (cells lyse, crystals form in vitro). If a delay is anticipated before analysis, the urine should be refrigerated. Refrigerated urine should always be brought to room temperature before testing.

A complete urinalysis consists of 1) evaluation of physical characteristics, 2) measurement of specific gravity, 3) dipstick analysis and 4) examination of sediment.

 

Equipment and Materials

Microscope

Refractometer

Slides

Urinalysis dipsticks

Urine sediment stain

Physical Characteristics of Urine

1. Evaluate and record urine color

Normal mammalian urine is yellow to amber. Urine volume and concentration affect the depth of the color.

Some examples of various urine colors and corresponding common possible causes:  

2. Evaluate and record urine turbidity

Fresh urine is clear to very slightly cloudy. Urine may become more cloudy if left standing or if refrigerated. The turbidity of the urine sample is reported as: clear, slightly cloudy, cloudy, opaque, or flocculent. Excess turbidity results from the presence of suspended particles in the urine. The cause can usually be determined based on the results of the microscopic urine sediment examination.

 

Common causes of abnormal turbidity include:

  • increased cells (RBC, WBC)

  • numerous crystals

  • bacteria

  • lipiduria (lipids often rise to the surface)

  • mucus (especially in horses)

  • semen

  • fecal contamination

 

3. Odor

Ammonia is formed from urea by bacterial action. An ammonia smell may be prominent in retained or old urine samples. An acetone small may suggest ketosis. Some drugs may impart a characteristic odor.

4. Volume

Urine volume may be estimated from urine specific gravity. In general, volume and specific gravity (S.G.) are inversely related in health and in most diseases. Exceptions include:

Diabetes mellitus. Polyuria and high S.G. coexist because of glucosuria.

Acute and chronic renal disease. Oliguria (↓ urine volume) may be accompanied by a lack of renal concentrating ability.  

       

5. Measure specific gravity (S.G.)

 

Specific gravity is the ratio of the refractive index of urine compared to water. Refractometry is the easiest method to measure urine S.G.Dipsticks are not as accurate. Glucose and protein may falsely ↑ urine S.G.

 

Knowledge of the hydration status is necessary to interpret the S.G. Urine S.G. can vary from 1.001 to 1.065 in most healthy animals but this range also includes values associated with renal abnormalities. S.G. has been inadequately studied in elephants and obtaining a baseline during health and evaluating sequential samples during illness is recommended.

 

Isosthenuria (fixed S.G.) is the constant maintenance of urine S.G in the range of the glomerular filtrate (1.008-1.012). Isosthenuria means the kidney is neither concentrating nor diluting urine.

 

Hyposthenuria is a S.G. < 1.008. In hyposthenuria the kidneys still have some water-balance function.

 

6. Perform dipstick analysis and record results (see charts in Appendix H).

  • Mix the urine

  • Dip the dipstick ; remove extra urine

  • Start timing

  • Compare to chart on bottle in good light

7. Urine sediment examination

  1. Centrifuge a fresh urine sample for 5 minutes at about 1500 RPM

  2. Remove supernatant

  3. Add 1-2 drops of stain to sediment

  4. Tap the bottom of the tube to mix

  5. Transfer one drop to a slide and place a coverslip

  6. Examine the entire coverslip at 10X and 40X

* Low maginification (10x): casts, large crystals, debris, parasitic ova are visible

* High magnification (40x): leukocytes, erythrocytes, epithelial cells, fat  droplets, small crystals, sperm, debris and bacteria are visible