This issue of Pediatric Annals addresses renal diseases in pediatric patients. Our Guest Editor, Robert B. Ettenger, MD, Professor of Pediatrics at the UCLA School of Medicine, and his coauthors provide us with information we should know about the causes and management of the most common of these diseases and the signs and symptoms with which they present in pediatric practice. Although such signs and symptoms are broad in their scope, we have come to depend on the urinalysis to provide initial clues to diseases affecting the urinary tract. Indeed, a urinalysis is included in the evaluation of all hospitalized infants, children, and adolescents and of almost all pediatric patients seen on an ambulatory basis who do not have readily definable illness (signs- and symptoms-wise) implicating the urinary tract.
Further, a urinalysis frequently is performed on asymptomatic pediatric patients as a screening test. The American Academy of Pediatrics (AAP) recommends that a screening urinalysis be performed on all patients sometime during infancy (the first year of life), early childhood (1 through 4 years), late childhood (5 through 12 years), and adolescence (13 through 20 years). l Many pediatricians perform screening urinalyses more often than the AAP recommends.
Whenever one considers screening asymptomatic individuals for any disease, several principles should be applied.2 Those principles that relate to screening urinalysis include:
* Screen only for conditions that can be diagnosed with certainty.
* Screen only for conditions that will benefit from early diagnosis and treatment.
* Use only screening tests that are known to be highly accurate.
* Be certain that positive screening findings are followed by appropriate diagnostic evaluations and treatment.
* Be certain that the screening test is cost effective for both the individual and the general population.
So, how do we judge the worth of screening urinalysis? First, we have to decide how to collect the urine specimen. For screening purposes, in the interests of minimal invasiveness, we must use voided urine specimens rather than specimens that are collected by catheterization or by suprapubic aspiration - methods used when clinical circumstances suggest that urinary tract disease, particularly infection, may be present. Voided urine specimens may be collected for screening by 1) voiding into a receptacle with prior cleansing of the urethral orifice and its surrounding structures, collecting the entire specimen, or 2) collecting a specimen caught in the receptacle at some point between the onset and completion of voiding (midstream, clean-catch specimen), which, presumably, is less likely to be contaminated by red and white blood cells and by organisms in the vicinity of the urethral orifice not removed by cleansing prior to voiding. The first method is the simplest to perform, by using a plastic bag pasted to the perineum in infants and a cup held in the standing position (for male children and adolescents) or the sitting position with the labia majora and minora spread apart (for female children and adolescents). However, this method is very likely to produce false-positive results. The second method, which is less likely to do so, requires assistance by a professional skilled in catching the midstream specimen, particularly in females whose labia must be spread apart during the voiding. Children and adolescents cannot be expected to do this properly, nor can their parents be instructed to do it easily. Thus, midstream, clean-catch specimen collection in pediatric patients requires a good deal of time and effort by professionals to ensure minimization of specimen contamination.
Second, once the specimen is collected, it must be examined properly. This ordinarily requires (for screening purposes in asymptomatic patients) only the use of a dipstick. The dipstick tests for the presence of protein, glucose, occult blood (intact erythrocytes, hemoglobin from hemolysed erythrocytes, and myoglobin produced by a variety of causes of muscle damage3), pH, and two possible indicators of urinary tract infection - nitrites produced by bacteria and leukocyte esterases released from destroyed leukocytes. Both of these can produce false-positive and false-negative results; false -positive protein and occult blood dipstick results also can occur. Glycosuria as an indicator of diabetes mellitus rarely is discovered with screening urinalysis in asymptomatic pediatric patients.
Some pediatricians take screening urinalysis one step further by examining the specimen for the presence of bacteria. This is done best by placing two drops of freshly obtained uncentrifuged urine on a sterile slide within a standardized marked area 1.5 cm in diameter. The specimen is air dried, Gram stained, and examined for bacteria microscopically, using the oil immersion lens.4 If bacteria are present, some clinicians recommend culturing the urine and treating the patient if the culture grows out 100CK)O or more colonies. Others consider treatment of asymptomatic bacteriuria contraindicated because 1) treatment may lead to greater risk for pyelonephritis and potential renal scarring because of the development of resistant organisms and 2) children who have bacteriuria do not have a high frequency of associated urinary tract structural anomalies that might lead to renal scarring and end-stage renal disease.5
All of this information about screening urinalysis for asymptomatic pediatric patients should prompt a review of the principles of screening noted above, considering that any of the positive findings on the urine dipstick or examination for bacteriuria probably should generate repeat screening before any further diagnostic tests are performed. Does screening urinalysis live up to these principles? I don't think so, not only for child health supervision visits, but also for pediatric patients who are hospitalized for illnesses not related to suspected urinary tract disease.6,7 The costs of follow-up, more sophisticated urinalyses, and other diagnostic tests of the urinary tract, as well as the anxieties they provoke in parents and patients, are too high, relative to the significance of their findings. In the long run, however, pediatric practitioners must answer this question for themselves.
1. Committee on Practice and Ambulatory Medicine. Recommendations for preventive health care. American Academy of Pediatrics News. July 1991.
2. Frankenburg WK, Thornton SM. Screening: general considerations. In: Hoekelman RA, Friedman SB, Nelson NM, Seidel HM1 eds. Primar» Pedíame Care. 2nd ed. Sr UiUiS1 Mo: Mosby-Yearbook Ine; 1992:21 1-212.
3. Yadin Q Hematuria in children. PeflW Ann. 1994;24:474-485.
4. Hobennan A, Wald ER, Reynolds EA, Penchansky L, Charron M. Pyuria and bacteriuria in urine specimens obtained by catheter from young children with fever. J Pediarr. 1994;124:513-519.
5. Ruley EJ1 Ongkingeo JR. Use of urinalysis and urine culture for screening. In: Hoekelman RA, Friedman SB1 Nelson NM, Seidel HM, eds. Primary Pediatric Care. 2nd ed. St Louis, Mo: Mosby-Year Book Ine; 1992:227-229.
6. Hermansen MC, Blodgett FM. Perspecrive evaluation of routine admission urinalyses. AmJ Dis Cm. 1981;135:126-130.
7. Mitchell N, Stapleton FB. Routine admission urinalysis examination in pediatric patients: a poor value. Pediatrics. 1990;86:345-349.