Test performance of urinanalysis and urine microscopy for the diagnosis of urinary tract infection: a meta-analysis

Williams GJ, Craig JC, Irwig L
Centre for Kidney Research, The Children’s Hospital Westmead, Sydney
Dept of Public Health and Community Medicine, University of Sydney

Urinary tract infection (UTI) is an important but problematic diagnosis in childhood. The reference standard for diagnosis is urine culture but this takes at least 24 hours to confirm or exclude infection. Because of the clinical importance of early diagnosis, tests such as microscopy for the detection of urinary white cells (pyuria) and reagent strips for leucocyte esterase and nitrite have been developed and used.

Many primary studies have assessed the performance of these tests. However the final results, clinical settings, thresholds and definitions have varied substantially, making application difficult. The aim of this study was to obtain an overall estimate of test performances of urine screening tests in children using meta-analytical techniques.

Methods included identifying eligible studies by searching MEDLINE (1966-2000) and EMBASE (1988-2000) using terms for urinary tract infection and bacteriuria. These were then combined with many terms for urine microscopy, urinalysis, and diagnostic reagent kits. The search was limited to children and adolescents. The overall test performance of each screening test was analysed using a summary receiver operating curve (sROC) using data points from each primary study.

The search found 1412 abstracts, these were reviewed and 249 titles appeared appropriate or ambiguous and were obtained for clarification. Fifty seven papers were eligible and have undergone data extraction. Twenty seven papers assessed nitrite (n = 56583), 16 assessed leucocyte esterase (n = 8885) and 20 papers examined pyuria (n = 56513). The quality of the articles was in general poor. Taking articles that examined nitrite as an example, studies with verification bias over estimated the diagnostic odds ratio (DOR) by 10.9 (0.9-138.2, 95% CI) times compared with studies not having verification bias. Non-blinded studies over estimated the DOR by 83.1 (2.6-2634.8, 95% CI) compared to blinded studies. Thus the quality of a study had a significant impact on the outcome.

The summary estimates for each screening test are presented below.

There is substantial information about the test performance of urinalysis and urine microscopy for diagnosing UTI in children. Studies are generally poorly done and this results in substantial over estimation of the true test performance. Nitrite, leucocyte esterase and pyuria are inaccurate indicators of urinary tract infection in children and should not replace urine culture for the diagnosis of UTI