Diagnosing urinary tract infections can be achieved by determining the white blood cell concentration of the patient’s urine, according to a new study.

“Previously recommended pyuria thresholds for the presumptive diagnosis of UTI in young infants were based on manual microscopy of centrifuged urine [but] test performance has not been studied in newer automated systems that analyze uncentrifuged urine,” wrote Pradip P. Chaudhari, MD, and his associates at Harvard University in Boston.

Dr. Chaudhari and his coinvestigators looked at all infants no older than 3 months of age, who were examined for UTI at a hospital at any time between May 2009 and December 2014. After 377 were excluded due to various issues with the urine sample collected for analysis, 2,700 infants were available for study ( Pediatrics. 2016;138[5]:e20162370 ).

Of these 2,700 infants with a median age of 1.7 months, 211 (7.8%) had a urine culture come back positive for UTI. Likelihood ratio (LR) positive and negative were calculated to determine the microscopic pyuria thresholds at which UTIs became more likely in both dilute and concentrated urine. A white blood cell to high-power field (WBC/HPF) count of 3 yielded an LR-positive of 9.9 and LR-negative of just 0.15, making it the cutoff for dilute urine samples. For concentrated urine samples, 6 WBC/HPF had an LR-positive of 10.1 and LR-negative of 0.17, making it the cutoff for those samples. Leukocyte esterase (LE) thresholds also were determined for dipstick testing, with investigators finding that any positive result on the dipstick was a strong indicator of UTI.

“The optimal diagnostic threshold for microscopic pyuria varies by urine concentration,” the authors concluded. “For young infants, urine concentration should be incorporated into the interpretation of uncentrifuged urine analyzed by automated microscopic urinalysis systems.”

There was no external funding for this study. Dr. Chaudhari and his coauthors did not report any relevant financial disclosures.


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