Can urine clarity exclude the diagnosis of urinary tract infection?

OBJECTIVES

To determine the association of clear urine by visual inspection with the absence of significant bacteruria, and to compare it with standard urinalysis.

METHODS

The study was performed in the emergency department of Children's Hospital Medical Center, Cincinnati, Ohio. It was a prospective, convenience sample of children <21 years of age who had catheterized or midstream clean-catch urine specimen collected for culture. Clinical findings including the presence or absence of fever, abdominal pain, dysuria, frequency, and urgency were collected for each patient. Urine was visually assessed for clarity by 2 independent observers using a standardized technique. Standard laboratory urinalysis and microscopy were also performed on all specimens. A positive urine culture was defined as >/=10(4) colony-forming unit (CFU)/mL of a urinary pathogen if obtained by catheterization and >/=10(5) CFU/mL if obtained by midstream.

RESULTS

Samples were obtained from 159 patients ranging in age from 4 weeks to 19 years. Females comprised 77% of the patients. One hundred ten of the samples (69%) were clear to visual inspection. There were a total of 29 positive cultures; however, 3 were in children with clear urine. The finding of clear urine on visual inspection had a negative predictive value of 97.3%. These results were similar to those obtained with standard urinalysis.

CONCLUSION

Clear urine on visual inspection cannot completely eliminate the possibility that a child has a urinary tract infection. However, it is a reproducible test that offers the advantages of being simple, fast, and inexpensive. The finding of clear urine should be considered a reasonable and relatively effective bedside screen for the presence of a urinary tract infection.