Rapid dipstick test for diagnosis of urinary tract infection

Absolute and relative accuracy of rapid urine tests for urinary tract infection in children: a meta-analysis

Rapid urine tests, such as microscopy, for bacteria and white cells, and dipsticks, for leucocyte esterase and nitrites, are often used in children that are unwell to guide early diagnosis and treatment of urinary tract infection. We aimed to establish whether these tests were sufficiently sensitive to avoid urine culture in children with negative results and to compare the accuracy of dipsticks with microscopy. Medline, Embase, and reference lists were searched. Studies were included if urine culture results were compared with rapid tests in children. Data were analysed to obtain absolute and relative accuracy estimates. Data from 95 studies in 95 703 children were analysed. Summary estimates for sensitivity and specificity for microscopy for Gram-stained bacteria were 91% (95% CI 80-96) and 96% (92-98), for unstained bacteria were 88% (75-94) and 92% (84-96), for urine white cells were 74% (67-80) and 86% (82-90), for leucocyte esterase or nitrite positive dipstick were 88% (82-91) and 79% (69-87), and for nitrite-only positive dipstick were 49% (41-57) and 98% (96-99). Microscopy for bacteria with Gram stain had higher accuracy than other laboratory tests with relative diagnostic odds ratio compared with bacteria without Gram stain of 8.7 (95% CI 1.8-41.1), white cells of 14.5 (4.7-44.4), and nitrite of 22.0 (0.7-746.3). Microscopy for white cells should not be used for the diagnosis of urinary tract infection because its accuracy is no better than that of dipstick, laboratory facilities are needed, and results are delayed. Rapid tests are negative in around 10% of children with a urinary tract infection and cannot replace urine culture. If resources allow, microscopy with Gram stain should be the single rapid test used.

The urine dipstick test useful to rule out infections. A meta-analysis of the accuracy

BACKGROUND

Many studies have evaluated the accuracy of dipstick tests as rapid detectors of bacteriuria and urinary tract infections (UTI). The lack of an adequate explanation for the heterogeneity of the dipstick accuracy stimulates an ongoing debate. The objective of the present meta-analysis was to summarise the available evidence on the diagnostic accuracy of the urine dipstick test, taking into account various pre-defined potential sources of heterogeneity.

METHODS

Literature from 1990 through 1999 was searched in Medline and Embase, and by reference tracking. Selected publications should be concerned with the diagnosis of bacteriuria or urinary tract infections, investigate the use of dipstick tests for nitrites and/or leukocyte esterase, and present empirical data. A checklist was used to assess methodological quality.

RESULTS

70 publications were included. Accuracy of nitrites was high in pregnant women (Diagnostic Odds Ratio = 165) and elderly people (DOR = 108). Positive predictive values were >/=80% in elderly and in family medicine. Accuracy of leukocyte-esterase was high in studies in urology patients (DOR = 276). Sensitivities were highest in family medicine (86%). Negative predictive values were high in both tests in all patient groups and settings, except for in family medicine. The combination of both test results showed an important increase in sensitivity. Accuracy was high in studies in urology patients (DOR = 52), in children (DOR = 46), and if clinical information was present (DOR = 28). Sensitivity was highest in studies carried out in family medicine (90%). Predictive values of combinations of positive test results were low in all other situations.

CONCLUSIONS

Overall, this review demonstrates that the urine dipstick test alone seems to be useful in all populations to exclude the presence of infection if the results of both nitrites and leukocyte-esterase are negative. Sensitivities of the combination of both tests vary between 68 and 88% in different patient groups, but positive test results have to be confirmed. Although the combination of positive test results is very sensitive in family practice, the usefulness of the dipstick test alone to rule in infection remains doubtful, even with high pre-test probabilities.

Urinary tract infection in the pediatric patient

Little attention has been focused on the identification of urinary tract infection (UTI) in young febrile children in the emergency department, despite recent information that suggests both a high prevalence and significant associated morbidity in this population. Most UTIs that lead to scarring or diminished kidney growth occur in children younger than age 4 years, especially babies in the first year of life. Overall, prevalence rates of UTI in febrile infants in the emergency department are approximately 3% to 5%, with higher rates for white girls, uncircumcised boys, and those without another potential source for fever. Prevalence and risk factors are given so that clinicians may identify those febrile children at particularly high or low risk of UTI for selective management. Culturing methods, urine screening tests, and culture interpretation are reviewed and management strategies based on these results are suggested.

Screening tests for urinary tract infection in children: A meta-analysis

OBJECTIVE

To review systematically and to summarize the existing literature regarding performance of rapid diagnostic tests for urinary tract infection (UTI) in children.

DESIGN

Systematic review and meta-analysis.

METHODS

Published articles reporting the performance of urine dipstick tests (leukocyte esterase [LE] and/or nitrite), Gram stain, or microscopic analysis of spun or unspun urine in the diagnosis of UTI in children </=12 years of age. Articles were identified through a comprehensive MEDLINE search, and those articles meeting a priori inclusion criteria were selected. Eligibility criteria included the use of urine culture as the reference standard, independent comparison of urine culture with the results of one of the screening tests, definition of positive screening test results provided, only pediatric patients included or evaluable separately, and both gold standard and screening test performed on all patients. For each test, heterogeneity of reported sensitivity and specificity of all studies was determined. The subgroups of studies with similar definitions of UTI and age of study subjects were analyzed separately to account for some of the differences in reported results. When significant unexplained heterogeneity among studies precluded simple combining of results, a summary receiver-operator characteristic curve was fitted for each screening test, from which pooled estimates of true-positive rate (TPR; ie, sensitivity) and false-positive rate (FPR; 1-specificity) were calculated.

PRIMARY RESULTS

A total of 1489 titles were identified by the MEDLINE search; 26 articles met all criteria for inclusion. There was significant heterogeneity among studies for nearly all tests for both TPR and FPR, which was explained only partially by the stringency of the definition of UTI or age of subjects studied. Based on the pooled estimates, the presence of any bacteria on Gram stain on an uncentrifuged urine specimen had the best combination of sensitivity (0.93) and FPR (0.05). Urine dipstick tests performed nearly as well, with a sensitivity of 0.88 for the the presence of either LE or nitrite and an FPR of 0.04 for the presence of both LE and nitrite. Pyuria had lower TPR and higher FPR: for presence of >5 white blood cells/high-power field in a centrifuged urine sample, the TPR was 0.67 and the FPR was 0.21, whereas for >10 white blood cells per mm(3) in uncentrifuged urine, the TPR was 0.77 and the FPR was 0.11.

CONCLUSIONS

Both Gram stain and dipstick analysis for nitrite and LE perform similarly in detecting UTI in children and are superior to microscopic analysis for pyuria.

Nitrite and nitrate analyses: a clinical biochemistry perspective

OBJECTIVE

To review the assays available for measurement of nitrite and nitrate ions in body fluids and their clinical applications.

DESIGN AND METHODS

Literature searches were done of Medline and Current Contents to November 1997.

RESULTS

The influence of dietary nitrite and nitrate on the concentrations of these ions in various body fluids is reviewed. An overview is presented of the metabolism of nitric oxide (which is converted to nitrite and nitrate). Methods for measurement of the ions are reviewed. Reference values are summarized and the changes reported in various clinical conditions. These include: infection, gastroenterological conditions, hypertension, renal and cardiac disease, inflammatory diseases, transplant rejection, diseases of the central nervous system, and others. Possible effects of environmental nitrite and nitrate on disease incidence are reviewed.

CONCLUSIONS

Most studies of changes in human disease have been descriptive. Diagnostic utility is limited because the concentrations in a significant proportion of affected individuals overlap with those in controls. Changes in concentration may also be caused by diet, outside the clinical investigational setting. The role of nitrite and nitrate assays (alongside direct measurements of nitric oxide in breath) may be restricted to the monitoring of disease progression, or response to therapy in individual patients or subgroups. Associations between disease incidence and drinking water nitrate content are controversial (except for methemoglobinemia in infants).

A urine analysis method suitable for children's nappies

BACKGROUND

Urinary tract infection in infancy continues to be underdiagnosed, despite its association with renal scarring and thus hypertension, renal failure, and other sequelae. Low ascertainment of urinary tract infections reflects the many difficulties in establishing a diagnosis, some of which could be eliminated by a simple, reliable method for preliminary investigation of children's urine.

AIM

To assess the accuracy of a new, simple method for testing urine for nitrite and leucocyte esterase, which could be applied to children in primary care.

METHODS

An in vitro study was carried out to compare the results of conventional urine analysis with urine analysis on urine soaked on to panty-liners, and with the laboratory investigation. Two urine analysis stick types were used (Boehringer Mannheim Nephur sticks and Bayer Multistix 8SG) and two brands of panty-liners. Analysis examined evidence of agreement and bias for different methods in addition to sensitivity, specificity, and negative predictive values for urine analysis.

RESULTS

Pressing urine analysis test sticks on to panty-liners soaked with urine achieved consistent results compared with the results of conventional dipstick urine analysis. At a prevalence of 21.8%, sensitivity and negative predictive values of urine analysis for laboratory confirmed urinary tract infection were 94% and 98%, respectively, for Boehringer sticks, and 76% and 93%, respectively, for Bayer sticks. At prevalences of 5% and 1% (prevalences that could be expected in primary care) Bayer sticks had negative predictive values of 98.7% and 99.7%, respectively, and Boehringer sticks had values of 99.6% and 99.9%, respectively.

CONCLUSIONS

Testing urine on panty-liners is accurate compared with conventional urine analysis. It may be possible to apply this method to testing unwell children presenting in primary care to identify those who require microbiological urine culture to confirm or eliminate a diagnosis of urinary tract infection.