What is your preferred method of urine collection in pediatric patients?

by
Kenneth T. Kwon, MD, FAAP, FAAEM
Director of Pediatric Emergency Medicine
Division of Emergency Medicine
UC Irvine Medical Center

The collection method of choice for urine specimens in the pediatric population varies depending on the clinical situation. The methods available include bladder (transurethral) catheterization, bag-collection, and suprapubic percutaneous bladder aspiration.

If a urinary tract infection (UTI) is suspected, the goal is to obtain the cleanest specimen possible. In cooperative older children and young adults, this is easily accomplished with a standard clean voided mid-stream specimen. In infants and small children, however, this method is not an option. Sterile bladder catherization is the best way to obtain urine in these patients if an infectious cause is being pursued. Although more invasive than bag-collection, catheterization is much more reliable in detecting UTIs, with sensitivity and specificity reaching 95% and 99% respectively (1). A good rule of thumb is to perform catheterizations on all non-toilet-trained patients when suspecting a UTI; older but uncoordinated or uncooperative toilet-trained patients should also be considered for catheterized specimens.

The bag-collection technique is unreliable when evaluating for UTIs and is not recommended. One study found a 56% contamination rate of bag urine specimens collected in an emergency department (2), and others estimate up to an 85% false-positive rate of urine culture specimens obtained from a bag (1). Some practitioners feel that a negative urinalysis from a bag-collection specimen can be helpful to rule out a UTI. However, keep in mind that in children under about two years of age, a large percentage (up to 50%) will have culture-proven urinary tract infections with a negative urinalysis. Thus, confirmatory urine cultures should be sent on all these cases, and bag specimens are inadequate for culture testing.

Suprapubic bladder aspiration is regarded as the gold standard when comparing urine collection methods. This technique is technically simple and used commonly with premature neonatal patients, but its use in other ages are minimal. Due to the perceived invasive nature of the procedure by both parents and clinicians, it is rarely used in the ED setting. Also, some debate exists whether obtaining an actual urine specimen is more reliable with this method compared with catheterization. One ED study showed the success rate of obtaining urine via suprapubic bladder aspiration was only 46%, compared with 100% via bladder catheterization (3). Because of variable failure rates and experiences with this technique, suprapubic aspiration in the ED should be considered in those rare cases in which attempts to physically pass a catheter transurethrally are unsuccessful.

If urine is being collected for purposes unrelated to infection, the sterility of the specimen is not as important. Thus a bagged urine may be an acceptable method of collection. Examples of these situations would include assessment of hydration status with urine specific gravity or toxicologic evaluation with urine metabolite screening.

References
1. Downs SM. Technical report: urinary tract infections in febrile infants and young children. Pediatrics 1999;103:e54.
2. Al-Orifi F, McGillivray D, Tange S, Kramer MS. Urine culture from bag specimens in young children: are the risks too high? J Pediatr 2000;137:221-6.
3. Pollack CV Jr, Pollack ES, Andrew ME. Suprapubic bladder aspiration versus urethral catheterization in ill infants: success, efficiency, and complication rates. Ann Emerg Med 1994;23:225-30.

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