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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.
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.
In this issue of Pediatrics, Chaudhari et al. share the results of a study of the impact of urine concentration on the optimal threshold in the new era of automated urinalysis. Centrifugation of urine specimens has long been standard laboratory practice, presumably performed to concentrate sediment and facilitate the detection of cellular elements and bacteria.
However, for the many sites that do not have machines for automated urinalyses (virtually all office practices, for example), the most important finding in this study may well be how well LE [leukocyte esterase] performs regardless of urine concentration. The optimal threshold for LE is not clear, however. The authors use “small” as their threshold for LE. At any threshold, can a negative urinalysis be relied on to exclude the diagnosis of UTI? A “positive” culture without inflammation evident in the urine is likely due to contamination, very early infection (rare), or asymptomatic bacteriuria (positive urine cultures in febrile children can still represent asymptomatic bacteriuria, because the fever may be due to a source other than the urinary tract).
If there are, in fact, some true UTIs without evidence of inflammation from the urinalysis, are they as harmful as those with “pyuria”?
Animal data demonstrate it is the inflammatory response, not the presence of organisms, that causes renal damage in the form of scarring. So the role of using evidence of inflammation in the urine to screen for who needs a culture seems justified on the basis not only of practicality at point of care and likelihood of UTI, but also sparing individuals at low to no risk of scarring from invasive urine collection. Moreover, using the urinalysis as a screen permits selecting individuals for antimicrobial treatment 24 hours sooner than if clinicians were to wait for culture results before treating. The urinalysis provides a practical window for clinicians to render prompt treatment. And Chaudhari et al. provide valuable assistance for interpreting the results of automated urinalyses.
Kenneth B. Roberts, MD , is a professor of therapeutic radiology at Yale University, New Haven, Conn. He did not report any relevant financial disclosures. These comments are excerpted from a commentary that accompanied Dr. Chaudhari and his associates’ study ( Pediatrics. 2016;138(5):e20162877 ).
In this issue of Pediatrics, Chaudhari et al. share the results of a study of the impact of urine concentration on the optimal threshold in the new era of automated urinalysis. Centrifugation of urine specimens has long been standard laboratory practice, presumably performed to concentrate sediment and facilitate the detection of cellular elements and bacteria.
However, for the many sites that do not have machines for automated urinalyses (virtually all office practices, for example), the most important finding in this study may well be how well LE [leukocyte esterase] performs regardless of urine concentration. The optimal threshold for LE is not clear, however. The authors use “small” as their threshold for LE. At any threshold, can a negative urinalysis be relied on to exclude the diagnosis of UTI? A “positive” culture without inflammation evident in the urine is likely due to contamination, very early infection (rare), or asymptomatic bacteriuria (positive urine cultures in febrile children can still represent asymptomatic bacteriuria, because the fever may be due to a source other than the urinary tract).
If there are, in fact, some true UTIs without evidence of inflammation from the urinalysis, are they as harmful as those with “pyuria”?
Animal data demonstrate it is the inflammatory response, not the presence of organisms, that causes renal damage in the form of scarring. So the role of using evidence of inflammation in the urine to screen for who needs a culture seems justified on the basis not only of practicality at point of care and likelihood of UTI, but also sparing individuals at low to no risk of scarring from invasive urine collection. Moreover, using the urinalysis as a screen permits selecting individuals for antimicrobial treatment 24 hours sooner than if clinicians were to wait for culture results before treating. The urinalysis provides a practical window for clinicians to render prompt treatment. And Chaudhari et al. provide valuable assistance for interpreting the results of automated urinalyses.
Kenneth B. Roberts, MD , is a professor of therapeutic radiology at Yale University, New Haven, Conn. He did not report any relevant financial disclosures. These comments are excerpted from a commentary that accompanied Dr. Chaudhari and his associates’ study ( Pediatrics. 2016;138(5):e20162877 ).
In this issue of Pediatrics, Chaudhari et al. share the results of a study of the impact of urine concentration on the optimal threshold in the new era of automated urinalysis. Centrifugation of urine specimens has long been standard laboratory practice, presumably performed to concentrate sediment and facilitate the detection of cellular elements and bacteria.
However, for the many sites that do not have machines for automated urinalyses (virtually all office practices, for example), the most important finding in this study may well be how well LE [leukocyte esterase] performs regardless of urine concentration. The optimal threshold for LE is not clear, however. The authors use “small” as their threshold for LE. At any threshold, can a negative urinalysis be relied on to exclude the diagnosis of UTI? A “positive” culture without inflammation evident in the urine is likely due to contamination, very early infection (rare), or asymptomatic bacteriuria (positive urine cultures in febrile children can still represent asymptomatic bacteriuria, because the fever may be due to a source other than the urinary tract).
If there are, in fact, some true UTIs without evidence of inflammation from the urinalysis, are they as harmful as those with “pyuria”?
Animal data demonstrate it is the inflammatory response, not the presence of organisms, that causes renal damage in the form of scarring. So the role of using evidence of inflammation in the urine to screen for who needs a culture seems justified on the basis not only of practicality at point of care and likelihood of UTI, but also sparing individuals at low to no risk of scarring from invasive urine collection. Moreover, using the urinalysis as a screen permits selecting individuals for antimicrobial treatment 24 hours sooner than if clinicians were to wait for culture results before treating. The urinalysis provides a practical window for clinicians to render prompt treatment. And Chaudhari et al. provide valuable assistance for interpreting the results of automated urinalyses.
Kenneth B. Roberts, MD , is a professor of therapeutic radiology at Yale University, New Haven, Conn. He did not report any relevant financial disclosures. These comments are excerpted from a commentary that accompanied Dr. Chaudhari and his associates’ study ( Pediatrics. 2016;138(5):e20162877 ).
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.
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.
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.
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.
FROM PEDIATRICS
Key clinical point:
Major finding: UTIs can be safely diagnosed if the patient has a pyuria threshold of at least 3 WBC/HPF in dilute urine and 6 WBC/HPF in concentrated urine.
Data source: Retrospective cross-sectional study of 2,700 infants younger than 3 months between May 2009 and December 2014.
Disclosures: No external funding for this study; authors did not report any relevant financial disclosures.
