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Veterinarian Technician October 2005 (Vol 26, No 10)

Urine Collection Techniques

by Sarah Okumura, MA, RVT, CVPM

    Key Points

    • Collection of quality samples is required in order to obtain accurate results from diagnostic tests.
    • Many urine collection techniques may harm the patient if performed improperly.
    • Careful attention to proper procedure and development of good hands-on skills can make urine collection easier, provide a better sample, and minimize patient risk.

    Have you ever heard the saying "gar­bage in, garbage out?" Using the proper technique for collecting and storing a urine sample can make a big difference in the reliability of test results. Mistakes that are made when a sample is collected, labeled, or stored can produce test results that are invalid or misleading, potentially resulting in an incorrect diagnosis and, therefore, inappropriate treatment.

    To provide quality patient care, technicians must learn to use proper technique when handling laboratory samples. An ideal urine sample should contain only those cells, microorganisms, and other matter that actually exist in the patient's bladder. The terms artifact and contaminant refer to matter that is inadvertently introduced into the sample.1 The presence of these extraneous substances affects the integrity of the sample. By using proper technique, technicians can obtain quality diagnostic samples. Urine samples should preferably be collected first thing in the morning, before the administration of any medications, and especial­ly before contrast cystography.

    Cystocentesis

    There are several methods for collecting urine, but the method most likely to yield an ideal sample is cystocentesis.2 This procedure involves inserting a sterile needle through the abdominal wall and into the lumen of the bladder, followed by withdrawal of urine directly from the bladder into a sterile syringe.3,4 When properly obtained, the sample should be free from cellular artifacts and microbial contaminants and, therefore, should be usable for any type of urine testing. However, improper cystocentesis can cause trauma to the bladder or abdominal tissues.2 This trauma can result in a sample that is contaminated with blood, tissue cells, or microorganisms and could cause serious injury to the patient. For these reasons, proper training and strict adherence to correct procedure are required when obtaining a sample using this method.

    Before attempting cystocentesis, the presence of urine in the bladder should be confirmed by palpation, radiography, or ultrasonography. A sterile 6- to 20-ml syringe with a 22-gauge needle should be prepared. A 1-inch needle can be used for cats and small dogs; however, a 1½ to 2 inch needle is preferred for larger patients.5 The procedure is performed with the patient restrained in dorsal or lateral recumbency or while in a standing position.5 Good restraint is imperative because movement during the procedure can result in injury to the patient. Most patients tolerate this procedure well, but a few may require sedation or a short-acting anesthetic. For maximum safety and the most contaminant-free sample, the skin of the ventrocaudal abdomen should be clipped and scrubbed. This is highly recommended for dirty animals. More commonly, the skin is simply wiped with 70% alcohol. This appears adequate in most cases.3,5 With one hand, the technician isolates the bladder and traps it in the caudal abdomen so that it cannot inadvertently move cranially. The needle is directed dorsocaudally at a 45° to 75° angle3,5 to the abdominal wall and inserted into the bladder near the ventral midline. On male dogs, the needle is inserted lateral to the prepuce.6 The syringe plunger is retracted to collect at least 5 ml of urine. It is important to release the negative pressure on the plunger before withdrawing the needle to avoid aspiration of blood or material from other areas of the abdomen.

    If the attempt to aspirate urine is unsuccessful, or if blood enters the syringe, the negative pressure on the plunger should be released and the needle withdrawn. Another attempt can be made using a fresh syringe and needle.6 Never redirect or reinsert the same needle within the abdominal cavity because this can cause organ laceration, contamination of the sample, and introduction of infectious material into sterile parts of the body.3,5

    An ultrasonography unit, if available, can be used to facilitate cystocentesis. The same procedure should be followed; however, the ultrasonogram allows the technician to visualize the bladder and more easily direct the needle.

    After the procedure, the patient should be given the opportunity to urinate. Minor leakage of urine through the bladder wall is a possible complication of cystocentesis, although it does not commonly cause clinical illness. To minimize leakage, some veterinarians recommend avoiding compression of the bladder for several hours. It is also preferable to avoid elective abdominal surgery for a few days to a week after cystocentesis because of the possibility of mild inflammation resulting from bladder trauma or leakage.

    Urethral Catheterization

    Catheterization is another method that can be used to collect urine. A plastic, rubber, or metal tube is inserted via the urethral opening and threaded into the bladder.6 This method has an advantage in that the bladder does not need to be palpable in order for the catheterization to be successful. When done correctly, catheterization should not result in microbial contamination of the sample.6 However, urine samples collected via catheterization are more likely to contain epithelial cells scraped from the urethra during catheter insertion. Catheterized samples are considered acceptable for all types of urine testing.6 Urethral catheter­ization can also be used for administration of radiographic contrast material, for relief of urethral obstructions, and to allow continuous urine drainage.7 Rough or unclean catheter insertion can result in irritation and infection of the patient's urethra or bladder.3 These complications can be avoided by following the proper procedures. The species and sex of the patient determine the type of catheterization procedure that should be performed.

    Technique for Male Dogs

    Urethral catheterization is easier to perform in male dogs than in females. The technician should prepare a 4- to 10-Fr4 sterile, flexible polypropylene or red rubber catheter. It is important to make sure the catheter is long enough for the size of the patient. The length can be estimated by holding the packaged catheter next to the dog in the position it will be in once the catheter is in place. Two partial cuts should be made in the paper cover of the catheter: The first cut should be about 2 inches from the tip, and the other about an inch lower.4 A pair of examination gloves, surgical prep solution (e.g., chlorhexidine or povidone solution), sterile water-soluble lubricant, and two 6- to 20-ml syringes are also needed. The use of lidocaine jelly in lieu of plain lubricant may increase patient comfort and ease of catheter insertion.

    The dog is placed in lateral recumbency with its upper rear leg pulled out of the way.4 An assistant extrudes the penis from its sheath and holds it for the duration of the procedure. The prepuce and the exposed part of the penis are gently cleaned with dilute antiseptic solution4,5 and rinsed with water or saline. The paper covering is removed from the tip of the catheter, and the second paper segment is loosened from the rest of the package. This segment is used as a handle so that the technician can avoid touching the sterile catheter.4 Sterile lubricant is placed on the catheter tip, and the catheter is inserted into the urethral opening. The catheter is advanced gradually, keeping the exposed portion protected by the paper wrapper. Once the catheter enters the bladder, urine should appear at the distal end of the catheter. The paper wrapper is removed, the first syringe is attached, and several milliliters of urine is withdrawn. The syringe containing the first aliquot of urine is removed, the second syringe is attached, and at least 5 ml of urine is collected in the second syringe. The sample in the second syringe will be less likely to be contaminated by bacteria and artifacts, so that sample is preferred if a culture or sediment examination is desired.6 If an adequate volume is collected, this second sample should be used for the entire urinalysis and the urine collected in the first syringe discarded. If not, the urine in the first syringe may be used for determination of specific gravity and chemical constituents.

    Resistance may be encountered while attempting to advance the catheter. If this occurs, the technician should make sure the penis is still extruded from the prepuce and that the catheter is actually in the urethra opening. It is normal to feel some resistance when the catheter reaches the os penis, when it reaches the ischial arch (the part of the urethra that curves around the pelvis), and occasionally at the level of the prostate gland,3 but gentle, steady pressure will most often allow the catheter to continue advancing. If the catheter still will not advance, a smaller size may be needed.6 It is important to never force a catheter because this may traumatize or even perforate the urethra.

    Technique for Female Dogs

    Female dogs are more of a challenge when placing a catheter because the opening to the urethra is located inside the vestibule beyond the vulva. For this procedure, a sterile 4- to 14-Fr red rubber, polypropylene, or rigid metal catheter should be prepared. Other supplies needed include a sterile vaginal speculum or otoscope, sterile gloves, surgical prep solution (e.g., chlorhexidine or povidone solution), sterile lubricant, and two 6- to 20-ml syringes.4

    The patient is restrained in a standing position4,6 or in sternal recumbency with its hind legs draped over the end of the table. The assistant holds the dog's tail out of the way during the procedure.6 The vulva is gently cleansed with antiseptic solution4,5 and rinsed with water or saline. Some veterinarians recommend flushing the vagina with saline or sterile water injected through a syringe. The vaginal speculum and the tip of the catheter are lubricated.6 Wearing sterile gloves, the technician inserts the speculum into the vulva,5 directing it dorsocranially to avoid the clitoral fossa, a blind pouch located on the ventral wall of the vestibule. The technician advances the instrument, looking for the urethral papilla, which is about 1½ to 2 inches inside the vagina on the ventral surface just cranial to the clitoral fossa.3 The urinary catheter is gently introduced into the urethral orifice and advanced into the bladder.6 The technician attaches the first syringe and withdraws several milliliters of urine. The syringe containing the first aliquot of urine is removed, the second syringe is attached, and at least 5 ml of urine are collected in the second syringe. As is true when placing a catheter in male dogs, the sample in the second syringe is preferred if a culture or sediment examination is needed because that sample is less likely to be contaminated by bacteria and artifacts.

    An alternative method for catheterization of female dogs is to locate the urethral opening manually by inserting a gloved finger into the vagina.3

    Technique for Male Cats

    Because catheterization of male cats often requires chemical restraint,4,7 this method is not commonly used for sample collection. In addition to urine collection, catheterization of male cats is frequently used to relieve urethral obstructions and to administer radiographic contrast materials.

    For catheterization of a male cat, a 3.5-Fr tomcat catheter should be prepared.4,7 Open-ended catheters are generally preferred for relief of urethral obstructions, whereas closed-end catheters are used more to collect samples or administer contrast materials. Sterile gloves, sterile lubricant, surgical prep solution (e.g., chlorhexidine or povidone solution), and two 6- to 20-ml syringes are also needed.

    The patient is restrained laterally with its hind legs pulled forward and its tail out of the way.4,7 The prepuce is gently cleansed with antiseptic solution and rinsed with water or saline. The tip of the catheter is lubricated. Using a thumb and forefinger, the technician extrudes the tip of the penis from its sheath. The catheter is introduced into the urethral opening and advanced into the bladder.6 Advancement of the catheter may be aided by allowing the penis to retract into the prepuce and applying traction to the penis. This will straighten the urethra, facilitating movement of the catheter.7 The urine specimen is then collected as in canine catheterization.

    Because of the painful nature of the procedure and the sometimes forceful manipulation required, catheterization of patients with an obstruction must be performed carefully while the patient is sedated or anesthetized. In addition, the procedure should be performed under the direction of a ­veterinarian.

    Technique for Female Cats

    Catheterization of female cats is the most challenging type of urethral catheterization for most technicians. As in male cats, sedation is frequently required7; however, some skilled technicians can perform this procedure in an unsedated patient. As in the case of female dogs, the urethral opening is internal to the vulvar opening, although in cats it is located much closer to the opening than in bitches. The required supplies and the restraint technique are similar to those used for male cats. A 3.5- to 5-Fr catheter is recommended.3,4,7

    The vulva is gently cleansed with antiseptic solution and rinsed with water or saline. Topical anesthetic (e.g., 2% lidocaine jelly, 0.5% proparacaine ophthalmic anesthetic solution) may be applied to the interior of the vulvar lips and vestibule to facilitate catheterization of nonsedated cats.7 (About two to three drops of either solution can be used, totaling no more than 0.3 ml of solution.) The tip of the catheter is lubricated with a sterile water-based lubricant (e.g., sterile water, KY jelly, lidocaine jelly). The lips of the vulva are pulled caudally and ventrally, and the catheter is inserted between the ventral vulvar lips along the ventral surface of the vestibule at the midline.7 Because of the small size of the cat's vestibule and vagina, the catheter is always inserted into the urethral orifice blindly (i.e., without using an instrument to help visualize the internal structures).4,6,7 Once the catheter has successfully entered the urethra and passed into the lumen of the bladder, urine is collected using the same technique as for male cats.

    In some cases, the veterinarian will elect to suture a catheter in place in a hospitalized patient to maintain the patency of the urethra. Otherwise, the catheter should be gently withdrawn from the patient as soon as the sample has been collected. As with all urethral catheterizations, it is important to allow the patient an opportunity to urinate normally after the procedure is finished.

    Collection of Voided and Expressed Samples

    Waiting for the patient to urinate may seem like the easiest and safest way to collect urine. However, this voided sample is most likely to be contaminated.2,3,6 Artifacts such as hair, dirt, plant material, and microorganisms from the patient's skin are common in voided or "free-catch" samples. Free-catch samples are suitable for basic procedures, such as analysis of the physical and chemical properties of the urine; however, they are not recommended for urine culture or examination of urine sediment.3,6

    To collect a voided sample from a dog, the vulva or prepuce is first cleansed with a mild antiseptic. The technician then takes a clean, labeled urine collection container with him or her when walking the patient outside. Once the patient begins to urinate, the container is placed into the urine stream.8 A cup holder, which can be easily constructed from a wire coat hanger, can make the collection process easier.6,8 A kitchen ladle can also be used. The technician should collect at least 5 ml of urine but withdraw the container before the patient finishes urinating.8

    Collecting a voided sample from a cat is more difficult. The cat must be confined in a cage with no litter in the litterbox8 or with special nonabsorbent litter. After the cat urinates, the sample can be collected from the litterbox with a syringe. Another method is to place plastic wrap over the litter to catch the urine.

    Samples can also be collected by manually expressing the patient's bladder, but this can be traumatic in conscious animals.3,6 When using this method, the bladder is palpated and isolated by grasping it with one or both hands. It is then manually compressed in a caudal direction.3 The stream of urine is collected in a clean container. Bladder expression is contraindicated in animals with urethral obstruction because it can cause bladder rupture.6 In addition, expressed samples are more likely to contain blood cells and excess epithelial cells as a result of the trauma caused by the procedure.3,6

    Handling and Processing Collected Samples

    Once a urine sample has been collected, it should be placed into a sealed, sterile container. Nonsterile samples can be stored in a clean (nonsterile) sealed container. Urinalysis should be performed within 30 minutes.6 Samples may be stored in a refrigerator for several hours if required but should be returned to room temperature (slowly) before testing. (Crystals may form in refrigerated samples. Most [but not all] of these crystals will dissolve when the sample is returned to room temperature.) Samples that must be stored for more than a few hours may require chemical preservatives to be added (e.g., 1 drop 40% formalin per ounce of urine).3,6

    All laboratory samples should be labeled with the patient's and owner's names. It is also advisable to label the sample with the date and time of collection and list which tests are to be conducted.

    Conclusion

    In order to obtain quality diagnostic urine samples, it is essential for technicians to use proper technique. Samples that are free of artifacts and contaminants can help the veterinarian determine a more accurate diagnosis.

    1. Blood DC, Studdert VP: Saunders Comprehensive Veterinary Dictionary, ed 2. Philadelphia, WB Saunders, 1999, pp 90-91, 273, 1061.

    2. Sirois M: Urinalysis, in Veterinary Clinical Laboratory Procedures. St. Louis, Mosby, 1995, pp 124-125.

    3. Osborne CA, Stevens JB: Collection of urine, in Handbook of Canine and Feline Urinalysis. St. Louis, Ralston Purina, 1981, pp 21-34.

    4. Bistner SI, Ford RB, Raffe MR: Routine diagnostic procedures, in Kirk and Bistner's Handbook of Veterinary Procedures and Emergency Treatment, ed 7. Philadelphia, WB Saunders, 1995, pp 486-492.

    5. Macintire DK, Drobatz KJ, Haskins SC, Saxon WD: Urologic emergencies, in Manual of Small Animal Emergency and Critical Care Medicine, ed 1. Philadelphia, Lippincott Williams & Wilkins, 2005, pp 226-231.

    6. Zinkl JG: Urinalysis, in Hendrix CM (ed): Laboratory Procedures for Veterinary Technicians, ed 4. St. Louis, Mosby, 2002, pp 215-222.

    7. Crow SE, Walshaw SO: Manual of Clinical Procedures in the Dog, Cat, & Rabbit, ed 2. Philadelphia, Lippincott Williams & Wilkins, 1997, pp 121-135.

    8. Pattengale P: Tasks for the Veterinary Assistant. Philadelphia, Lippincott Williams & Wilkins, 2005, pp 272-274.

    References »

    NEXT: When the Client Asks: "Geriatric Changes in Dogs and Cats"

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