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Veterinarian Technician January 2007 (Vol 28, No 1) Focus: Basic Skills

Microscopic Examination of Urine Sediment

by Margi Sirois, EdD, MS, RVT, Elaine Anthony, MA, CVT

    In human medicine, microscopic examination of urine sediment is usually done only when patients are symptomatic for urinary tract disease or when the gross and chemical urine examination denotes abnormalities. In veterinary clinics, however, this procedure is performed as part of routine patient evaluations. In most mammals, normal urine contains little or no sediment.

    A consistent approach is crucial to ensuring the accuracy and reliability of test results. Each staff member in the clinic should perform sample collection, processing, and examination using the same standard protocol.

    Samples for sediment examination should be collected after several hours of water deprivation because concentrated samples tend to increase the chance of finding formed elements.1 Therefore, the first morning sample is most commonly used. To improve the validity of the results, the sample volume should be 5 to 10 ml.2 Smaller volumes will provide less accurate results. Whenever a sediment examination is performed on smaller sample volumes, this should be noted on the laboratory records because normal values are based on larger sample volumes.

    The sediment examination must be performed within 30 minutes to an hour of urine collection to minimize the possibility of artifactual changes in the sample.2 Common artifacts that may be seen in samples not processed quickly include bacterial overgrowth and changes in crystalline material, cast structure, and cellular detail. If urine sediment examination is to be delayed, the gross and chemical examinations should be performed and then the sample should be preserved either by refrigerating it or by adding a preservative such as formalin or toluene to it.1

    Common Findings in Canine and Feline Urine Sediment

    Urine sediment may contain a variety of cells, casts, crystals, and miscellaneous components (e.g., parasite ova).

    Blood and epithelial cells are frequently found in urine sediment. The presence of these elements may be due to pathologic processes or may result from the use of certain collection methods.

    Urinary casts are cylindrical structures formed from a matrix of protein released by damaged renal cells. Casts form in slow-moving filtrate at acidic pH and take on the shape of the tubule.2 Casts may contain cellular material trapped within the matrix. There are five main types of urinary casts: hyaline, cellular, granular, waxy, and fatty casts.2 Waxy and fatty casts are rarely seen. Waxy casts are usually wide and smooth with blunt ends. Fatty casts, which are seen in the presence of nephrotic syndrome or diabetes mellitus, contain lipid material trapped in the hyaline protein matrix.2 Cast fragments may also be seen.

    Crystalluria is the presence of crystals in urine.2 Crystals are a common finding in urine sediment; however, only a few types of crystals are of consequence.2 The formation of crystals is determined by the amount of the substance in the urine and the solubility of the particular crystal type.2 In addition, crystals are also affected by the pH and specific gravity of the urine.

    A variety of additional components may be seen in urine sediment. These may be artifacts introduced during sample collection, or they may be contaminants from the environment. However, the presence of these miscellaneous components in the urine may indicate pathologic abnormalities.

    Conclusion

    Microscopic examination of urine sediment is a rapid, easy-to-perform diagnostic procedure that can provide valuable information to the clinician. To be of greatest value, efforts must be made to standardize collection and evaluation techniques and reporting of results.

    Recommended Reading

    Graff L: A Handbook of Routine Urinalysis. Philadelphia, Lippincott, Williams & Wilkins, 1983.

    Osborne C, Stevens J: Urinalysis: A Clinical Guide to Compassionate Patient Care. Shawnee Mission, KS, Bayer, 1999.

    1. Zinkl JG: Urinalysis, in Hendrix CM (ed): Laboratory Procedures for Veterinary Technicians. St. Louis, Mosby, 2002, pp 215-255.

    2. Anthony E, Sirois M: Microbiology, cytology, and urinalysis, in Sirois M (ed): Principles and Practice of Veterinary Technology, ed 2. St. Louis, Mosby, 2004, pp 248-275.

    References »

    NEXT: On the Cover: "A Talk with Harold Davis, Jr., BA, RVT, VTS (ECC, Anesthesia)"

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