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Urinalysis for the practitioner

01 August 2016, at 1:00am

Rand Wilson shows how veterinary surgeons in practice can develop the ability to run effective urinalyses more frequently, gaining valuable diagnostic information.

URINALYSIS (U/A) IS A SOMEWHAT overlooked and under- utilised diagnostic test, which should be more often considered a vital component of the minimum baseline database for evaluating the health of our patients.

Urinalysis has the added benefits of being minimally invasive, economically cost- effective and as the general public and pet owners are aware of its value in the human medicine realm, it is not an unknown test. 

This review will give the practising veterinarian the ability to run effective urinalyses more frequently, gaining valuable diagnostic information. You will be able to run U/As in-house or be able to get the most information from your urine samples submitted to the diagnostic laboratory.

There are four primary factors/parts to consider for maximising your U/A results. The first thing to consider is how to collect the urine sample.  

Timing is the second factor to consider. Generally, collect samples early in the day if possible. Why? This is often the most concentrated sample of the day, with better preservation of cells, casts and crystals. 

Timing of testing: ideally, analyse urine as soon after collection as possible. This is the primary advantage of doing in-clinic/in-house U/A. If delayed analysis, then refrigerate the sample. Note: you should be aware that if delayed analysis (ex: 12-24 hours), the results will be altered.

Macroscopic analysis is the third consideration of the U/A. This is an important part of the analysis, which is often the only part done by practitioners. This is only a part of the full U/A. The macroscopic analysis has two parts: the Gross evaluation and the semi- quantitative chemical analysis (Dipstick test).

  • Gross includes colour (yellow, orange, red, etc.), clarity (clear, cloudy, turbid, opaque, etc.) and specific gravity (SG) using a refractometer (Figure 1) – do not use dipstick pad results for SG. Note: having a good quality and calibrated refractometer is critical to accurately documenting this parameter and essential for a complete U/A. SG is an important parameter which allows determination of renal concentrating ability. 
  • Semi-quantitative analysis with urine chemistry strips: there are several key points to remember with dipsticks. Ignore the leukocyte, urobilinogen and nitrite pad results in both dogs and cats. These have been shown to be inaccurate, misleading, and invalid in animal U/A. PH, protein, glucose, ketones, blood and bilirubin are valid and should be recorded.

Pay attention to the recommended timing listed on the bottle of sticks for reading the results on these pads. In addition, please remember that 1+ or less protein on these pads may not be clinically relevant, and that any level of protein on the dipstick needs to be interpreted in conjunction with a microscopic analysis and correlation to any pyuria/inflammation. Also, the blood pads will detect both ruptured (haemoglobin) and intact red cell presence.

Microscopic analysis is the fourth part of the U/A. Overall, this evaluation is at least equal to or often a more important part of the U/A, compared to chemistry analysis. When analysing an in-house U/A, prepare a urine spun sediment slide. This can be a cover-slipped wet mount slide using a drop of re- suspended sediment, after centrifuging an aliquot of urine at slower speeds. It is best to standardise the amount of urine at your clinic if possible (example: 2, 5, 10ml).

Try to use this same amount for each patient. Examine the slide at 10x and 40x, unstained if you’re able to do so.

Sedi-stain can be used, but bear in mind this can alter the interpretation, and sedi-stain often becomes contaminated with debris, bacteria, even fungi.

Check for any cells present, and record the type and numbers, as well as identify micro-organisms, crystals and casts. Establish a routine quantitative comparison analysis for your clinic.

The easiest and simplest way is using a “1-4+” scheme, or “few, mild, moderate, many” scheme.

This allows a more accurate determination of the pathologic relevance of your findings. An example would be 1+ WBCs seen or few seen = not significant pyuria/not clinically relevant; versus 4+ WBCs seen or many seen = marked pyuria/highly clinically relevant.

When sending your U/A to a diagnostic laboratory, it is recommended to refrigerate the sample in a plain tube, and a sterile tube if culturing it.

Microscopic analysis is done in the laboratory on unspun urine using an inverted microscope examination with organisms, crystals, casts and cells identified and counted, for generally a more accurate representation of the U/A microscopy.

You will receive a report with similar quantitative evaluation of the microscopic findings listing 1-4+ of all the following: RBCs, WBCs, epithelial cells, micro-organisms, crystals, casts, other (sperm, yeast, contaminants, etc.).