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Perform urine culture if UTI suspected despite absence of pyuria

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Recognize limitations of urinalysis: Get a culture

Shaikh et al. demonstrate that certain urinary pathogens fail to reliably elicit pyuria. In 1,181 children where both a urine culture and concomitant urinalysis were performed, only 87% of the time was pyuria found in the setting of a positive culture. The authors further found that Enterococcus, Klebsiella, and Pseudomonas species were less likely to elicit pyuria or a positive leukocyte esterase test despite causing a urinary tract infection.

So how does the urinalysis help? More pointedly, why do a urinalysis? The report by Shaikh et al. agrees with a previously published meta-analysis that reveals pyuria to be absent in at least 10% of urines that culture positive. For a condition as common as UTI, this is too high a false-negative rate. Shaikh et al. conclude that a urine culture should be obtained in all children suspected of UTI. Indeed, the AAP guidelines are consistent with this statement. The AAP guidelines recognize that a clinician may have a low level of suspicion for UTI and may choose not to treat. However, given recent analyses of the utility of urinalysis and the report by Shaikh et al., it is difficult to see how a negative urinalysis might reassure a clinician if there are signs of a UTI. Hence, if one is considering treating for presumptive UTI, a culture is needed. If one is considering waiting and not treating, but suspects a UTI, a culture is still needed. Shaikh et al. conclude that new biomarkers are needed if we really want help with the “point of care” testing. Although we wait for new biomarkers, we should recognize the limitations of a negative urinalysis and still get that urine culture.

Dr. Aaron Friedman is the former dean of the University of Minnesota Medical School, Minneapolis. These comments are excerpted from a commentary accompanying Dr. Shaikh and his associates’ report (Pediatrics. 2016. doi: 10.1542/peds.2016-1247). Dr. Friedman did not report any relevant financial disclosures or sources of external funding.


 

FROM PEDIATRICS

References

Urine cultures should be performed in all children clinically suspected of having a urinary tract infection (UTI), results of a study in Pediatrics suggest.

That’s because pyuria may be absent in some children with certain uropathogens.

“Clinicians rely heavily on the degree of pyuria when making a presumptive diagnosis of UTI [but] lack of pyuria on an initial urinalysis may result in delayed diagnosis and delayed antimicrobial therapy,” explained Dr. Nader Shaikh of the University of Pittsburgh and his associates. “We hypothesized, based on some preliminary data in adults, that gram-positive organisms would cause less inflammation of the urinary tract and consequently cause less pyuria on urinalysis than infections caused by gram-negative organisms, in which pyuria is observed in the vast majority of cases.”

Dr. Nader Shaikh

Dr. Nader Shaikh

Dr. Shaikh and his coinvestigators looked at patients under the age of 18 years admitted to the Children’s Hospital of Pittsburgh at the University of Pittsburgh Medical Center between 2007 and 2013 with a UTI. Of 46,158 relevant hospital visits over the course of the study period, 1,181 children were ultimately selected for inclusion. Urine samples were tested for the presence of uropathogens, followed by analysis for the presence of pyuria, defined as having 5 or more white blood cells per high-powered field or at least 10 white blood cells per mm3 of urine (Pediatrics. 2016. doi: 10.1542/peds.2016-0087).

Only 150 subjects (13%) did not have pyuria; the remaining 1,031 (87%) of subjects did. Escherichia coli was found in 999 of the 1,181 (85%) subjects included, of which 892 (89%) had pyuria. Additionally, of the 27 children found to have Staphylococcus saprophyticus, all had pyuria. High rates of pyuria also were found in children whose urine had Proteus species and Enterobacter species uropathogens: 25 of 31 (81%) and 13 of 15 (87%), respectively.

However, the presence of three other pathogens suggested a lower association between pyuria and UTI. Pseudomonas aeruginosa was found in 13 children, of which 8 (62%) had pyuria; similarly, those with Enterococcus species uropathogens had a 54% chance of having pyuria (19 of 35) and those with Klebsiella species had a 74% chance (34 of 46). The takeaway, therefore, is that pyuria may not always be present in cases of UTI, especially if these pathogens are the cause of it; in fact, “the odds of pyuria were three to five times lower” with these pathogens, compared with E. coli.

“The most recent American Academy of Pediatrics guideline suggests that pyuria should be present when diagnosing a UTI [but] only 90% of children with UTI exhibit pyuria even when the urine specimen is collected by bladder catheterization or suprapubic aspiration,” Dr. Shaikh and his associates found, adding that the “findings of our study offer an additional explanation for the absence of pyuria – some uropathogens may not elicit a strong host inflammatory response – [and] suggest that bedside biomarkers that are more sensitive and specific than pyuria are needed to improve the accuracy of early diagnosis.”

There was no outside funding involved with this study. Dr. Shaikh and his coauthors did not report any relevant financial disclosures.

dchitnis@frontlinemedcom.com

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