Original contributionDipstick urinalysis and the accuracy of the clinical diagnosis of urinary tract infection
Introduction
Many studies that have investigated the accuracy of dipstick urinalysis in detecting urinary tract infection (UTI) have done so without also considering the process of clinical assessment 1, 2, 3, 4, 5, 6, 7, 8, 9.
The diagnosis of UTI is difficult because of the inconsistent relationship between symptoms, pyuria, and bacteriuria 10, 11, 12, 13, 14, 15, 16, 17, 18. Symptoms usually associated with UTI may occur in other conditions such as chlamydial urethritis or vaginitis 10, 11. Frequency, urgency, and incontinence are common in the elderly population and have been reported equally in those with and without bacteriuria (12).
Dipstick urinalysis detects leukocyte esterase (LE), nitrites, blood, and protein. LE is a polymorph enzyme and, as such, only a surrogate marker for UTI, and not all urinary pathogens produce nitrites (13). Many disorders beside UTI cause proteinuria or hematuria (19). Previous studies report a wide variation in the sensitivity and specificity of the components of dipstick urinalysis in detecting UTI 1, 2, 3, 4, 5, 6, 7, 8, 9, 14, 20.
In forming estimates of the probability of disease, clinicians are influenced by personal experience or published articles that may suffer from biases of their own 21, 22.
Given the aforementioned problems in the diagnosis of UTI, the aim of this study was to determine whether dipstick urinalysis significantly augmented the accuracy of clinical assessment in the diagnosis of UTI in symptomatic patients.
Section snippets
Setting
Between January and April 1999, consecutive patients were prospectively recruited from an adult tertiary referral center Emergency Department (ED) in which 40,000 patients are treated annually. Twenty physicians participated.
Subjects and specimens
All patients with symptoms or signs possibly due to a UTI were eligible for study. Patients were excluded if they were on antibiotics, if they had stopped antibiotic use in the previous week, had inadequately completed questionnaires, had no urine culture, were known to
Patient characteristics
Of the 627 patients recruited, 227 (36%) patients were excluded for the following reasons: current antibiotic use (73), inadequately completed questionnaires (60), mixed Gram-negative and normal flora growth on urine culture (54), no urine culture sent (23), antibiotic use in the past week (15), and known UTI on presentation (2). This left 400 patients eligible for study, all of whom had urine sent for formal processing in the microbiology laboratory. Table 1 shows the patient characteristics
Discussion
This study specifically examined whether dipstick urinalysis provided clinicians with information that added to the diagnostic accuracy of their prior clinical assessment. While many previous studies have documented the diagnostic performance of dipstick urinalysis alone, this study demonstrates that dipstick urinalysis significantly augments clinical assessment in diagnosing UTI in symptomatic patients (Table 5, Figure 1) 1, 2, 3, 4, 5, 6, 7, 8, 9.
Sox showed that diagnostic tests have large
Summary
We found that dipstick urinalysis provided information to clinicians that significantly improved their accuracy at diagnosing UTI. For those patients with very few symptoms or classic symptoms, the test is unlikely to alter the clinical impression. In these cases, a treatment decision does not require dipstick urinalysis. We advise clinicians to utilize this test when their clinical assessment is equivocal or if uncertainty exists about a patient’s low or high probability designation. Depending
Acknowledgements
The authors thank the emergency department staff, including emergency department assistants, nursing staff and medical staff, the staff of the clinical microbiology laboratory, and Antony Ugoni (BSc Hons, MScStat) for his aid in the statistical analysis of data.
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