correct me if i am wrong but from what i remember about statistics, the sensitivity and specificity of any test depends on the pre-test probability. below is a nice summary i found online and attached is the table from that paper (it would not paste over). from this and others i have read, urine dips are not too good on patients who don't report symptoms like kids and the elderly. let me know what you think
Urine Dipstick for Diagnosing Urinary Tract Infection
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Am Fam Physician. 2006 Jan 1;73(1):129-132.
Clinical Question
How accurate is the urine dipstick for diagnosing urinary tract infection?
Evidence-Based Answer
The sensitivity and specificity of the urine dipstick varies somewhat with the setting and population, as does its recommended interpretation. Women with classic urinary tract infection (UTI) symptoms have a high pretest probability of infection, and use of the dipstick adds little to the diagnosis. In women with nonspecific urogenital symptoms, positive or negative dipstick results may require a backup urine culture depending on the clinical situation. In low-risk patients with a low pretest probability of UTI, the urine dipstick alone is useful to exclude infection if both nitrites and leukocyte esterase are negative. [Strength of recommendations: C, all recommendations based on meta-analyses of cohort studies not addressing patient-oriented outcomes]
Evidence Summary
A systematic review1 summarized the evidence on the diagnostic accuracy of the urine dipstick test for urinary tract infection, comparing test performance in various practice settings including outpatient primary care, emergency department, and inpatient care. Test performance also was estimated in the general population, including but not limited to children, pregnant women, older patients, and urology patients.1 Sensitivity using nitrites and/or leukocyte esterase was highest in the outpatient primary care setting (90 percent) and lowest in pregnant women (68 percent). Specificity was lowest in the outpatient primary care setting (65 percent). Table 11,2 discusses the performance of the urine dipstick test for diagnosing UTI in selected populations.
The clinical utility of the dipstick depends on the pretest probability of a UTI. In general, a negative test in a patient with a low pretest probability based on clinical presentation rules out disease, whereas it may not for a patient with a higher pretest probability. Conversely, a positive test may adequately confirm disease for a patient with classic symptoms of UTI and a high pretest probability, but not for a patient with a more confusing clinical picture and a lower pretest probability.
One systematic review2 reported that the pretest probability of UTI in otherwise healthy women with classic UTI symptoms (e.g., dysuria and frequency) is 60 percent. In women with classic symptoms who do not have any vaginal discharge or irritation, the pretest probability of UTI increases to 90 percent.2 Patients presenting with at least one poorly defined symptom (such as vaginal complaints) had a pretest probability of UTI of 50 percent. In this setting, a positive dipstick increased the probability of a UTI to 81 percent whereas a negative dipstick reduced the probability to 23 percent.2
Urinary complaints in children are commonly caused by noninfectious problems. Two meta-analyses1,3 found that the pretest probability of UTI in children was between 5 and 20 percent. A completely negative dipstick reduces the probability of a UTI to 5 percent in this setting, whereas a positive leukocyte esterase or nitrite increases the probability to only 58 percent.1 These patients therefore require further diagnostic confirmation (e.g., with a urine culture). A second meta-analysis4 of diagnosis in children suggests that a dipstick testing positive for both nitrite and leukocyte esterase provides strong evidence in favor of UTI (likelihood ratio = 28.2). This study also confirms the usefulness in ruling out disease with a dipstick negative for both nitrites and leukocyte esterase.4
Recommendations from Others
Evidence-based guidelines from the University of Michigan5 and the Institute for Clinical Systems Improvement6 support the approach of managing suspected UTI by telephone in women with typical symptoms of UTI, no vaginal symptoms, and no major comorbidities. A guideline from the Cincinnati Children’s Hospital Medical Center7 recommends a backup urine culture in children with suspected UTI, even if the dipstick or urine microscopy is negative.
Clinical Commentary
In women with classic UTI symptoms, particularly in the absence of vaginal symptoms, the probability of a UTI is so high that empiric treatment may be considered without dipstick testing. This might allow treatment by telephone, without necessitating a patient visit resulting in improved cost savings and patient convenience. In a patient with nonspecific complaints such as dysuria and vaginal discharge, a dipstick might be useful. In low-risk patients with a low pretest probability of UTI, the dipstick adequately rules out infection when both leukocyte esterase and nitrites are negative. This also has the benefit of cost containment because fewer urine cultures are needed in low-risk patients. Given the more serious consequences of a missed diagnosis of UTI in children, a backup urine culture is recommended.
OLIVIA RAE WRIGHT, M.D.
Southwest Washington Medical Center
Vancouver, Washington;
SARAH SAFRANEK, M.L.I.S.
University of Washington Health Sciences Libraries
Seattle, Washington
Address correspondence by e-mail to Olivia Rae Wright, M.D., owright@swmedctr.com. Reprints are not available from the authors.
Author disclosure: Nothing to disclose.
REFERENCES
1. Deville WL, Yzermans JC, van Duijn NP, Bezemer PD, van der Windt DA, Bouter LM. The urine dipstick test useful to rule out infections. A meta-analysis of the accuracy. BMC Urol. 2004;4:4.
2. Bent S, Nallamothu BK, Simel DL, Fihn SD, Saint S. Does this woman have an acute uncomplicated urinary tract infection?. JAMA. 2002;287:2701–10.
3. Huicho L, Campos-Sanchez M, Alamo C. Metaanalysis of urine screening tests for determining the risk of urinary tract infection in children. Pediatr Infect Dis J. 2002;21:1–11.
4. Whiting P, Westwood M, Watt I, Cooper J, Kleijnen J. Rapid tests and urine sampling techniques for the diagnosis of urinary tract infection (UTI) in children under five years: a systematic review. BMC Pediatr. 2005;5:4.
5. Urinary tract infection. Ann Arbor, Mich.: University of Michigan Health System; 2005. Accessed online October 12, 2005, at:
www.guideline.gov/summary/summary.aspx?ss=15&doc_id=7407.
6. Uncomplicated urinary tract infection in women. Bloomington, Minn.: Institute for Clinical Systems Improvement, 2004. Accessed online October 12, 2005, at:
guideline.gov/summary/summary.aspx?ss=15&doc_id=5570&nbr=3767.
7. Evidence based clinical practice guideline for medical management of first time acute urinary tract infection in children 12 years of age or less. Cincinnati, Ohio: Cincinnati Children’s Hospital Medical Center, 2005. Accessed online October 12, 2005, at:
www.guideline.gov/summary/summary.aspx?ss=15&doc_id=7272.
Attachments:TABLE 1.docx (15.49 KB)
