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What tests do health-care professionals use to diagnose UTIs in children?
Establishing an accurate diagnosis (vs. a presumptive diagnosis) includes determining the causative bacteria of the infection, its antibiotic sensitivity profile, and determining whether any anatomical or functional risk factors are present that might predispose the child to the current infection. Such information is crucial to establish the individual's risk for recurrent urinary tract infections, which can predispose to scarring of the kidney and possibly renal failure (end-stage kidney disease, requiring either dialysis or renal transplant).
The physical examination of a child with suspected urinary tract infection should start with the vital signs (temperature, pulse, breathing rate, and blood pressure, which is often measured with the vital signs). The presence of fever (especially over 102.2 F or 39 C) is highly correlated with the presence of a UTI. Blood pressure and assessment of height and weight provide helpful reassurance if normal or stable long-term renal function. Visual examination of the abdomen for enlargement related to potentially oversized kidney(s) or bladder is important. Tenderness during palpation of the abdomen (especially the suprapubic region containing the bladder) or the flank area (where the kidneys are situated) is very helpful in establishing the diagnosis.
Examination of the genitalia is also very important to see if there is evidence of vaginal irritation (redness, discharge, evidence of trauma or foreign body). An uncircumcised male infant (especially with a foreskin that is difficult to retract) is more likely to experience a UTI when compared to a population of similar infant boys who have been circumcised. Lastly, consideration of other conditions that might be responsible for fever and abdominal pain is important.
An abnormal urinalysis (including microscopic examination) may be indicative of a urinary tract infection. However, the urine culture is mandatory in confirming the diagnosis of a UTI. The culture provides both the exact bacterial cause as well as the antibiotic sensitivity profile to successfully treat the infection. In addition, studies have demonstrated a relatively short list of bacteria that commonly cause UTIs. A UTI caused by abnormal bacteria should be a source of concern.
In a toilet-trained child, a clean-catch urine specimen should provide a reliable specimen for culture. A non-toilet-trained child or an uncircumcised boy whose tight foreskin may lead to potential urine specimen contamination should have the specimen obtained by a sterile catheterization. An alternative approach to catheterization is called "suprapubic bladder aspiration." This safe procedure involves passing a small needle through the skin into the urine-filled bladder cavity and aspiration of urine into the attached syringe. Collection of urine in a "urine bag" is not recommended. Some studies have indicated an 85% false-positive rate of UTI diagnosis with this method, prompting unnecessary laboratory and diagnostic studies as well as inappropriately prescribed antibiotic therapy.
Regardless of the mechanism chosen to obtain a child's urine specimen, it is very important to examine the urine as soon as possible since a delay can increase the risk of both false-negative and false-positive results.
Other laboratory studies (for example, complete blood count) are generally not helpful, and their nonspecific values do not provide differentiation between the more significant kidney infection (pyelonephritis) and a less concerning bladder infection (cystitis).