Reappraising the value of urine leukocyte esterase testing in the age of nucleic acid amplification

Background: The leukocyte esterase (LE) test has a limited role in the determination of empiric therapy for male patients screened for urethritis because of its poor positive predictive value in low (<5%) prevalence settings. The recent advent of nucleic acid amplification testing of first-void urine (FVU) has dramatically increased the ease with which widespread screening for Chlamydia trachomatis and Neisseria gonorrhoeae can be performed, but the costs of such testing may be prohibitive. The LE test may therefore have a role in management of urethritis because of its high negative predictive value. Objectives: To determine the sensitivity, specificity, and positive and negative predictive value of LE testing for the diagnosis of N. gonorrhoeae and C. trachomatis in male FVU specimens in a low-prevalence urban setting using a commercial polymerase chain reaction (PCR) as the gold standard. Methods: Data were obtained on men presenting to an urban sexually transmitted disease clinic over a 16-month period, Patients were included if an FVU had been tested for the presence of LE using a rapid dipstick, read by an automated urine analyzer, and the sample (either an FVU or urethral swab) had then been processed for the detection of N. gonorrhoeae and C. trachomatis by PCR. Results: Of 301 assessable patients, there were 14 cases of gonorrhoea, 21 cases of chlamydia, and 1 case of dual infection detected by PCR, Most men (245/301; 81.4%) were asymptomatic, of whom 12 of 245 (4.9%) had an infection detected compared with 24 of 56 (42.9%) in the symptomatic men (P < 0.001), Using a "greater than or equal to trace" cutoff, the overall value for the sensitivity of the LE test was 77.8% (95% confidence interval, 60.4-89.3), specificity 80.8% (75.4-85.2), positive predictive value 35.4% (25.2-47.1), and negative predictive value 96.4% (92.8-98.3), Conclusions: The negative predictive value of the LE test may be of use in determining which patients should proceed to specific diagnosis by nucleic amplification methods (e.g., PCR or ligase chain reaction). By limiting testing to patients with positive LE results, costs savings mag be made, enabling the technology to be used in a wider community setting. The value of the LE test in higher prevalence populations with access to nucleic amplification testing remains to be established.