Practical urinalysis in the cat: 2: Urine microscopic examination 'tips and traps'

[Urinalysis in dogs and cats, part 2: Urine sediment analysis]

Examination of the urine sediment is part of a routine urinalysis and is undertaken in order to identify insoluble particles in the urine. This procedure is mainly used in the context of diagnostic evaluation of urinary tract diseases, but may also be useful for the diagnosis of systemic diseases and intoxications. Analysis of fresh urine is recommended as changes in cell morphology, cell lysis and in vitro crystal formation may occur in the course of its storage. Manual urine sediment analysis is still performed in many veterinary practices. Native wet-mount preparations are suitable for the identification and quantification of urine sediment particles. The examination of stained wet-mount preparations or air-dried smears may be necessary to further differentiate cells and to identify bacteria. For several years, automatic urine sediment analyzers have been available in veterinary medicine. These save considerable time and staff resources, however verification of the automatically generated results by an experienced observer remains necessary. Urine sediment particles that are frequently identified and clinically relevant include red blood cells, white blood cells, different types of epithelial cells, crystals, and casts as well as bacteria. Furthermore, parasite eggs, fungal hyphae, lipid droplets, spermatozoa, fibres, hair, mucus, plant parts or environmental contaminations may be found in the urine sediment and result in a complication of the result interpretation.

Comparison of six microscopic methods and two operators for estimation of white and red blood cells in canine urine sediment

BACKGROUND

Little information is currently available about the analytical variability of urinalysis.

OBJECTIVE

We aimed to compare results obtained by two operators using six microscopic methods in the quantification of urinary leukocytes (WBC) and erythrocytes (RBC).

METHODS

Forty urine samples (10 mL) were centrifuged (450g, 5 minutes) and resuspended in 0.5 mL of supernatant. Two operators with different expertise in urinalysis interpreted sediment results using the six methods, obtained by combining the use of microscope slides (Slide) or counting chambers (Chamber) with three different techniques: bright-field (BF) microscopy, phase-contrast (PC) microscopy, and stained sediment (SS) evaluations. The mean WBC and RBC counts from 10 fields (Slide) or squares (Chamber) observed at 400× were used to calculate the difference and agreement between operators and methods. We also estimated the concordance between methods in classifying microhematuric or pyuric samples.

RESULTS

Operator 2 counted significantly lower WBC counts using Slide+BF (P = 0.009) and Slide+PC (P = 0.001) than Operator 1, whereas no inter-operator differences were recorded for RBC counts. The concordance between the operators ranged from "good" to "very good." No differences or biases were found for WBC counts among the methods, and concordances were "good" to "very good"; proportional biases were found for RBC counts between Slide+BF vs Slide+SS and Slide+PC vs Slide+SS. Concordance measurements for RBC counts ranged from "good" to "very good."

CONCLUSIONS

All methods yielded good reproducibility among operators, although stained SS evaluations allowed better identification of WBC by the inexperienced operator. However, we suspected that the SS preparations affected RBC counts. All other methods yielded reproducible WBC and RBC counts.

Urinalysis in dog and cat: A review

Urinalysis is the examination of normal and abnormal constituents of urine. It is an easy, cheap, and vital initial diagnostic test for veterinarians. Complete urinalysis includes the examination of color, odor, turbidity, volume, pH, specific gravity, protein, glucose, ketones, blood, erythrocytes, leukocytes, epithelial cells, casts, crystal, and organisms. Semi-quantitative urine analysis with urine dipsticks, as well as an automatic analyzer, provides multiple biochemical data. Contamination is almost entirely avoided if the protocols for ensuring a proper sample have been followed, as mentioned still consideration must be given to the likelihood of contamination, even if the sample is correctly obtained. Interpretation of urinalysis will be doubtful if the knowledge of the interference is limited. Well-standardized urinalysis, when correlated in the context of history, clinical findings, and other diagnostic test results, can identify both renal and non-renal disease. This paper reviews significance of different components of urinalysis of dog and cat, such as collection, storage, examination, interpretation, and common causes of error in the result.