Laboratory testing and diagnosis
The 2011 AAP guideline on UTI5 and its reaffirmation in 20164 suggest that UTI is best diagnosed when a combination of bacteriuria (of at least 50,000 colony-forming units (CFUs) and pyuria are present.15
Significant bacteriuria is operationally defined differently by various authors, and methodologic issues preclude saying which mechanism is best for a diagnosis of UTI.16
However growth of uropathogenic bacteria in the following amounts has been considered significant in practice and the pediatric literature for some time:4,5,17,18
· Clean voided: ≥100,000 CFU/mL.
· Catheter: ≥50,000 CFU/mL (10,000-50,000 CFU/mL may indicate an increased risk of gram-positive or mixed organisms).19
· SPA: growth of any uropathogenic bacteria.
There is also discussion of whether or not cutoffs mentioned above are appropriate because as many as 20% of UTIs might be missed using conventional cutoffs.20 As a result, there is a need for other diagnostic tests.
Pediatricians rely on pyuria to make a diagnosis of UTI. However, as many as 10% of children with a positive urine culture and symptoms of UTI may lack pyuria on urinalysis.3 Pyuria may not be present because an inflammatory response has not yet had time to develop or the particular pathogen (Enterococcus, Klebsiella species, or Pseudomonas aeruginosa) may not as commonly produce pyuria.
In a 2016 study published in Pediatrics, Shaikh and colleagues looked at more than 1181 children diagnosed with UTI at the Children’s Hospital of Pittsburgh of UPMC, Pennsylvania, emergency department (ED) between 2007 and 2013. Pyuria was present in 87% of the children and absent in 13%. This pattern held true when the researchers’ analysis looked at only patients diagnosed via bladder catheterization.
Children diagnosed with an organism other than Escherichia coli were significantly less likely to have pyuria—3 to 5 times less likely when Enterococcus, Klebsiella species, or P aeruginosa was the diagnosis.3 Further, it was unlikely that asymptomatic bacteriuria accounted for these findings. Rather, the more likely explanation for the lack of pyuria is that some uropathogens do not produce a strong inflammatory response.