A 24-year-old healthy woman calls her primary care physician, complaining of a burning pain when urinating and increased urinary frequency for several hours. She has had 2 previous urinary tract infections (UTIs), and this episode seems “just like the other ones.” She is sexually active with 1 partner and uses a condom with spermicide. She denies fever, back pain, nausea, vomiting, vaginal discharge, and hematuria.
A 20-year-old woman presents to your office, complaining of urinary frequency, burning on urination, and vaginal discharge. She has had occasional fevers and chills but denies nausea, vomiting, and back pain. She is sexually active with 1 partner, takes oral contraceptive pills, and intermittently they use condoms. Physical examination shows her to be in mild discomfort and febrile but without tenderness in her costovertebral areas. Pelvic examination demonstrates minimal white vaginal discharge, no vaginal lesions or rashes, and no cervicitis. Her dipstick urinalysis result is negative for leukocyte esterase, nitrite, and blood.
Why Is This an Important Question to Answer With a Clinical Examination?
Acute uncomplicated UTIs are common in women, accounting for more than 7 million office visits annually in the United States1 and affecting half of all women at least once during their lifetimes.2 A recent study of sexually active young women found the incidence of cystitis to be 0.5% to 0.7% per year.3 In aggregate, the direct costs of these infections have been estimated to be $1.6 billion annually in the United States.4
One might anticipate that the management of acute uncomplicated UTI would be relatively uniform because the causative agents and in vitro susceptibilities are known, and therapeutic responses to antimicrobials have been studied carefully.2, 5, 6, and 7 Unfortunately, the evaluation and treatment of acute uncomplicated UTI in women vary substantially among physicians,8 likely reflecting the limitations of routine diagnostic assessments. When done correctly, however, the history taking and physical examination can be used in the initial evaluation of patients suspected of having an acute uncomplicated UTI and can guide the selection of additional diagnostic and therapeutic strategies.2, 7
Several types of UTI are described by their location: urethritis, cystitis, pyelonephritis, and perinephric abscess. The usual reference standard for diagnosing UTI is the presence of “significant” bacteria in a clean-catch or catheterized urine specimen, most commonly defined as the isolation of at least 105 colony-forming units (CFU) per milliliter of a single uropathogen.2 In women who present with symptoms of cystitis or urethritis (lower UTI), it has been suggested that the best diagnostic criterion for clean-catch urine is the isolation of uropathogens in concentrations as low as at least 102 CFU/mL.9
Uncomplicated UTIs occur in individuals who have a normal urinary tract system. A UTI in an individual with a functional or anatomic abnormality of the urinary tract (including a history of polycystic renal disease, nephrolithiasis, neurogenic bladder, diabetes mellitus, immunosuppression, pregnancy, indwelling urinary catheter, or recent urinary tract instrumentation) is considered complicated and may have a higher risk of treatment failure.10 Differentiating between these types of UTIs is important because uncomplicated infections are usually cured with simple antimicrobial regimens.10
The prevalence of asymptomatic bacteriuria (significant bacteriuria without symptoms of UTI) in women of reproductive age is approximately 5%.11, 12 This value represents the pretest probability of disease (the probability of UTI before any diagnostic tests are applied). Several historical features, symptoms, and signs associated with acute UTI may be useful for screening, allowing the clinician to estimate the probability of UTI in a patient after taking a medical history and performing a physical examination. Historical features such as a history of UTI, recent sexual activity, or contraceptive use identify individuals at greater risk of developing a UTI. Symptoms of an acute infection include burning or pain on urination (dysuria), frequent voiding of small volumes of urine (frequency), the urge to void immediately (urgency), and the presence of blood in the urine (hematuria). Discomfort in the lower abdominal area is also consistent with a UTI. In contrast, patients who report vaginal discharge or irritation are less likely to have a UTI and more likely to have vaginitis or cervicitis. The presence of fever and suprapubic or costovertebral angle tenderness may indicate infection of the upper urinary tract.
Vaginal infections (eg, Gardnerella, Candida albicans, Trichomonas), sexually transmitted diseases that may lead to pelvic inflammatory disease (eg, Chlamydia trachomatis, Neisseria gonorrhoeae), and other sexually transmitted diseases (eg, herpes simplex virus) that mimic symptoms of UTI are considered separate from UTIs. These infections are caused by different microbes; limited to female genital structures, with a unique set of complications if untreated; and require different forms of treatment.13 Differentiating between vaginal infections, sexually transmitted diseases, and UTIs can be difficult because symptoms and signs commonly overlap.13
We searched the English-language medical literature to determine the accuracy and precision of the clinical examination in women suspected of having an acute UTI. We searched MEDLINE for articles from 1966 through September 2001, with a search strategy similar to that used by other authors in this series.14 Search terms included “urinary tract infection,” “diagnostic tests,” “physical examination,” and “sensitivity and specificity.” This computerized search was supplemented with a manual review of the bibliographies of all identified articles, additional “core” articles (identified a priori as articles used to develop a recent guideline for treating acute uncomplicated UTI in women), 3 commonly used clinical skills textbooks,15, 16, and 17 and contact with experts in the field. One of the authors (B.K.N.) initially screened the titles and abstracts of the search results. Two of the authors (S.B. and B.K.N.) then independently reviewed and abstracted data from articles identified as relevant.
We included studies in our review if they contained original data on the accuracy or precision of the symptoms or signs in diagnosing acute uncomplicated UTI in healthy women. Articles were excluded if they evaluated infants, children or adolescents, pregnant women, nursing home patients, or patients with complicated UTI or contained insufficient or incomplete data to allow calculation of likelihood ratios (LRs) for signs or symptoms of acute UTI.
We also chose to include articles on the dipstick test in this analysis because it is commonly used in the clinical setting and provides an immediate result that can be incorporated with other elements of the initial clinical assessment. During our search, we discovered that a previous systematic review evaluated the diagnostic accuracy of the dipstick test.18 Because this was a high-quality review (meeting all 6 criteria of a previously published guideline for evaluating systematic reviews),19 we chose to use the information about the accuracy of the dipstick test synthesized in that article.
Quality Assessment of Included Articles
The methodological quality of the included articles was assessed independently by 2 authors (S.B. and B.K.N.), using criteria adapted from other authors in this series.14, 20 Disagreements were resolved by a third author (S.S.). Level 1 studies included those with an independent blind comparison of signs or symptoms with a gold standard among a large number (≥50) of consecutive patients suspected of having a UTI. Level 2 studies were similar to those in level 1 but involved a smaller number of patients (<50). The remaining levels are described in Table 1-7.
We used published raw data from the studies that met our criteria to calculate summary measures for the LRs for components of the clinical examination for UTI. LRs are related to sensitivity and specificity (positive likelihood ratio [LR+] = sensitivity/[1 – specificity]; negative likelihood ratio [LR–] = [1 – sensitivity]/specificity) but are more clinically useful because they can be used to generate posttest probabilities.21 A random effects model was used to generate conservative summary measures and confidence intervals (CIs) for the LRs and estimates of disease prevalence.22, 23 Uncertainty in these measures is reflected in the broad CIs around the estimates. When a summary LR included studies of lower quality, we conducted sensitivity analyses to examine the influence of excluding lower-quality studies on the summary LR and the effectiveness score, a measure of the discriminatory power of a diagnostic test.24
We found 9 studies of the 464 identified by the search that satisfied all inclusion criteria (Table 51-1). Six studies25, 26, 27, 28, 29, and 30 reported the accuracy of 1 or more symptoms in the diagnosis of UTI, 2 studies31, 32 reported the accuracy of symptoms and physical examination signs, and 1 study reported the accuracy of self-diagnosis.33
Table 51-1Studies Used to Determine the Accuracy of Clinical History and Physical Examination in Women Suspected of Having Urinary Tract Infection |Favorite Table|Download (.pdf) Table 51-1 Studies Used to Determine the Accuracy of Clinical History and Physical Examination in Women Suspected of Having Urinary Tract Infection
|Source, y ||Methodologic Qualitya ||Inclusion Criteria ||No. of Patients ||Mean Age, yb ||Incidence of UTI, % ||Setting and Country |
|Gallagher et al,25 1965 ||Level 1 ||Women with symptoms of UTI ||130 ||… ||59 ||Urban clinics in New Zealand |
|Mond et al,26 1965 ||Level 1 ||Women with symptoms of UTI ||83 ||… ||45 ||General practice in the United Kingdom |
|Lawson et al,27 1973 ||Level 1 ||Women aged 15 55 y with symptoms of UTI ||343 ||… ||47 ||Two general practices in the United Kingdom |
|Dans and Klaus,28 1976 ||Level 1 ||Women reporting dysuria ||84 ||26 ||46 ||US adult walk-in clinic |
|Komaroff et al,29 1978 ||Level 4 (including women without symptoms suggestive of UTI) ||Women with symptoms suggestive of urinary or vaginal infection ||821 ||24 ||12 ||US ambulatory care facility |
|Nazareth and King,30 1993 ||Level 1 ||Women aged 16-45 y presenting with frequency or dysuria ||54 ||29 ||28 ||Two general practices in suburban London |
|Gupta et al,33 2001 ||Level 5 (no urine culture in women without symptoms) ||Women >18 y with a history of recurrent UTI ||172 ||23 ||NA ||US university-based clinic |
|Symptoms and Physical Examination Findings |
|Wong et al,31 1984 ||Level 4 (including patients without symptoms suggestive of UTI) ||Women with symptoms of UTI or with both UTI and vaginal complaints and random selection of women with vaginitis or STD ||53 Cases, 139 controls ||… ||NA ||US STD clinic |
|Wigton et al,32 1985 ||Level 3 (retrospective chart review) ||Retrospective review of patients who had urine culture in emergency department ||216 In training set, 236 in validation set ||… ||NA ||US emergency department |
The studies were published between 1965 and 2001 and generally involved patients with 1 or more symptoms of a UTI who presented to outpatient clinics. The summary prevalence of UTI in the 5 studies that included only symptomatic patients and used an appropriate gold standard was 48% (95% CI, 41%-55%),25, 26, 27, and 28, 30 indicating a high probability of disease for women who met the studies’ inclusion criteria. In all of the included studies, UTI was defined by the presence of at least 10 000 or 100 000 CFU/mL of a single uropathogen, except for the most recent study, which used a cutoff of at least 100 CFU/mL.33
Five25, 26, 27, and 28, 30 of the 8 studies describing the accuracy of symptoms were of high quality (level 1). Both studies31, 32 describing the accuracy of the physical examination were of lower quality (levels 3 and 4), as was the study examining self-diagnosis (level 5).33 Reasons for quality scores lower than level 1 are shown in Table 51-1. Two of the lower-quality studies29, 31 included patients with vaginal discharge but without symptoms of UTI and therefore did not specifically address the diagnostic accuracy of signs and symptoms exclusively in women suspected of having a UTI.
The precision of a symptom or sign refers to the degree to which different examiners report the same finding (eg, dysuria present or absent) when interviewing or examining the same patient. None of the identified studies described the precision of the medical history or physical examination in the diagnosis of UTI, possibly because the questions and examination procedures were considered to be unambiguous. For example, most of the historical items consist of asking yes or no questions such as, Are you having burning or pain with urination? Variations in interview style and the phrasing of questions may affect results, but there is no information from the identified studies to suggest particular wording of questions or specific ways to examine patients for the 2 relevant physical examination signs (costovertebral angle tenderness and vaginal discharge).
Eight studies 25, 26, 27, 28, 29, 30, 31, and 32 examined the accuracy of 9 symptoms for predicting the presence of UTI. These symptoms and the corresponding LR+ and LR– from each study are shown in Table 51-2. Three of the symptoms (flank pain, abdominal pain, fever) had both summary LR+ and summary LR– with CIs overlapping 1.0 and are therefore not useful as diagnostic tests.
Table 51-2Clinical Signs and Symptoms in the Prediction of Urinary Tract Infectiona |Favorite Table|Download (.pdf) Table 51-2 Clinical Signs and Symptoms in the Prediction of Urinary Tract Infectiona
|Study ||LR+ (95% CI) ||LR– (95% CI) |
|Gallagher et al25 ||1.3 (1.1-1.6) ||0.28 (0.12-0.67) |
|Mond et al26 ||1.4 (1.1-1.8) ||0.22 (0.07-0.70) |
|Lawson et al27 ||1.2 (1.0-1.5) ||0.77 (0.60-0.99) |
|Nazareth and King30 ||1.1 (0.87-1.5) ||0.58 (0.14-2.4) |
|Komaroff et al29 ||3.2 (2.7-3.7) ||0.16 (0.09-0.27) |
|Wong et al31 ||3.0 (2.0-4.6) ||0.53 (0.39-0.73) |
|Wigton et al32 (training set) ||1.4 (1.1-1.8) ||0.69 (0.52-0.92) |
|Wigton et al32 (validation set) ||1.1 (0.81-1.4) ||0.94 (0.72-1.2) |
|Summary ||1.5 (1.2-2.0) ||0.48 (0.31-0.74) |
|Gallagher et al25 ||0.96 (0.87-1.1) ||1.6 (0.44-6.0) |
|Mond et al26 ||0.99 (0.90-1.1) ||1.2 (0.17-8.0) |
|Lawson et al27 ||1.1 (1.0-1.3) ||0.65 (0.43-0.97) |
|Dans and Klaus28 ||1.4 (1.0-2.1) ||0.63 (0.37-1.1) |
|Nazareth and King30 ||1.0 (0.80-1.3) ||0.87 (0.20-3.8) |
|Komaroff et al29 ||10 (7.8-13) ||0.07 (0.04-0.16) |
|Wong et al31 ||5.2 (3.1-8.7) ||0.45 (0.32-0.63) |
|Wigton et al32 (training set) ||1.8 (1.0-3.5) ||0.87 (0.75-1.0) |
|Wigton et al32 (validation set) ||1.3 (0.80-2.0) ||0.93 (0.80-1.1) |
|Summary ||1.8 (1.1-3.0) ||0.59 (0.35-1.0) |
|Gallagher et al25 ||1.8 (0.80-3.9) ||0.88 (0.75-1.0) |
|Mond et al26 ||2.9 (1.0-8.6) ||0.81 (0.66-1.0) |
|Nazareth and King30 ||6.5 (1.4-30) ||0.70 (0.49-1.0) |
|Wigton et al32 (training set) ||1.6 (0.82-3.3) ||0.92 (0.82-1.0) |
|Wigton et al32 (validation set) ||1.4 (0.60-3.4) ||0.96 (0.88-1.1) |
|Summary ||2.0 (1.3-2.9) ||0.92 (0.86-0.98) |
|Gallagher et al25 ||2.4 (1.2-4.9) ||0.75 (0.61-0.92) |
|Mond et al26 ||2.8 (0.77-9.9) ||0.87 (0.73-1.0) |
|Lawson et al27 ||0.65 (0.32-1.3) ||1.0 (0.97-1.1) |
|Nazareth and King30 ||0 (0-175) ||0.92 (0.78-1.1) |
|Wigton et al32 (training set) ||1.5 (0.74-3.0) ||0.94 (0.84-1.0) |
|Wigton et al32 (validation set) ||2.1 (1.0-4.6) ||0.89 (0.80-0.99) |
|Summary ||1.6 (1.0-2.6) ||0.9 (0.9-1.0) |
|Flank Pain |
|Gallagher et al25 ||1.1 (0.64-1.7) ||0.98 (0.77-1.2) |
|Mond et al26 ||1.1 (0.54-2.2) ||0.97 (0.74-1.3) |
|Lawson et al27 ||1.1 (0.87-1.4) ||0.92 (0.77-1.1) |
|Summary ||1.1 (0.90-1.4) ||0.84 (0.82-1.1) |
|Lower Abdominal Pain |
|Gallagher et al25 ||0.99 (0.76-1.3) ||1.0 (0.63-1.6) |
|Mond et al26 ||1.2 (0.67-2.1) ||0.91 (0.65-1.3) |
|Wong et al31 ||1.5 (0.90-2.4) ||0.87 (0.71-1.1) |
|Summary ||1.1 (0.90-1.4) ||0.89 (0.75-1.0) |
|Vaginal Discharge |
|Dans and Klaus28 ||0.80 (0.53-1.2) ||1.3 (0.82-2.0) |
|Komaroff et al29 ||0.11 (0.06-0.19) ||12 (8.9-16) |
|Wong et al31 ||0.43 (0.27-0.69) ||1.9 (1.4-2.5) |
|Summary ||0.34 (0.14-0.86) ||3.1 (1.0-9.3) |
|Vaginal Irritation |
|Komaroff et al29 ||0.09 (0.05-0.18) ||6.2 (5.0-7.6) |
|Wong et al31 ||0.63 (0.37-1.1) ||1.2 (1.0-1.5) |
|Summary ||0.24 (0.06-0.93) ||2.7 (0.88-8.5) |
|Back Pain |
|Wigton et al32 (training set) ||1.7 (1.1-2.6) ||0.80 (0.67-0.96) |
|Wigton et al32 (validation set) ||1.6 (1.1-2.5) ||0.81 (0.68-0.97) |
|Nazareth and King30 ||0.78 (0.25-2.4) ||1.1 (0.79-1.5) |
|Summary ||1.6 (1.2-2.1) ||0.83 (0.74-0.94) |
|Gupta et al33 ||4.0 (2.9-5.5) ||0 (0-0.08) |
|Vaginal Discharge on Physical Examination |
|Wong et al31 ||0.81 (0.66-0.99) ||1.9 (1.1-3.3) |
|Wigton et al32 (training set) ||0.32 (0.12-0.89) ||1.1 (1.0-1.2) |
|Wigton et al32 (validation set) ||0.44 (0.19-1.0) ||1.1 (1.0-1.2) |
|Summary ||0.69 (0.50-0.94) ||1.1 (1.0-1.2) |
|Costovertebral Angle Tenderness on Physical Examination |
|Wigton et al32 (training set) ||2.0 (1.2-3.4) ||0.82 (0.71-0.95) |
|Wigton et al32 (validation set) ||1.4 (0.8-2.4) ||0.91 (0.79-1.0) |
|Summary ||1.7 (1.1-2.5) ||0.86 (0.78-0.96) |
|Dipstick Urinalysisb |
|Hurlbut and Littenberg18 ||4.2 ||0.3 |
Four symptoms significantly increased the probability of UTI: dysuria, frequency, hematuria, and back pain. Four symptoms significantly decreased the probability of UTI: absence of dysuria, absence of back pain, a history of vaginal discharge, and a history of vaginal irritation. The symptoms with the greatest diagnostic power were a history of vaginal discharge (LR, 0.34) and a history of vaginal irritation (LR, 0.24); both of these symptoms substantially reduced the probability of UTI.
One study examined the accuracy of self-diagnosis and included 172 women in a university based practice with recurrent UTI (more than 2 UTIs in the past year).33 During the study period, 88 of the women reported 172 episodes of self-diagnosed UTI; 144 of these episodes (84%; 95% CI, 77%-90%) were found to have positive urine culture results. Additionally, 64 women reported mild symptoms that they did not self-diagnose as UTI and another 20 women never had symptoms. In this population of patients, the positive predictive value of self-diagnosis was high (84%). LRs for self-diagnosis can be calculated assuming that the women with mild symptoms or no symptoms correctly self-diagnosed with no infection (these women did not have a urine culture, but all symptoms resolved spontaneously). If this assumption is true, the LR for a positive self-diagnosis is 4.0, whereas the LR for a negative self-diagnosis is 0 (Table 51-2).
One study29 provided information to calculate the LRs for combinations of symptoms in the diagnosis of UTI (Table 51-3). In this study, the presence of dysuria and frequency without vaginal discharge or irritation was associated with a high LR (25). Conversely, the LR for the combination of vaginal discharge or irritation without dysuria was low (0.3). Although the LRs from this study must be interpreted with caution because of the study's low quality score (level 4), the observed LRs were similar to those calculated by combining the individual summary LRs from the other studies (Table 51-3).
Table 51-3Likelihood Ratios for Combinations of Symptoms |Favorite Table|Download (.pdf) Table 51-3 Likelihood Ratios for Combinations of Symptoms
| || ||Based on Data From Komaroff et al29 |
|Symptom Combinations ||Overall LR Using Combinations of Individual Symptomsa ||Posttest Probability of UTI, %b ||Summary LRc |
|Dysuria present ||1.5 ||77 || |
|Frequency present ||1.8 || || |
|Vaginal discharge absent ||3.1 || || |
|Vaginal irritation absent ||2.7 || || |
|Overalld ||23 || ||25 |
|Dysuria absent ||0.5 ||4 || |
|Vaginal discharge or irritation present ||0.3 or 0.2 || || |
|Overall ||0.1-0.2 || ||0.3 |
|Dysuria or frequency present ||1.5 or 1.8 ||9 || |
|Vaginal discharge or irritation present ||0.3 or 0.2 || || |
|Overall ||0.3-0.5 || ||0.7 |
Two studies31, 32 reported the accuracy of 2 physical examination signs for the presence of UTI. Both studies were of relatively low quality, and therefore the summary data do not represent strong evidence of the true accuracy of these signs (Table 51-2). The presence of costovertebral angle tenderness increases the likelihood of infection, but the LR is only weakly predictive and similar in magnitude to the related symptom of back pain. The presence of vaginal discharge on examination decreases the likelihood of UTI (LR, 0.69), although it is less powerful than the LR for the symptom of vaginal discharge reported by the patient (0.34).
Because a high-quality systematic review examining the accuracy of the dipstick urinalysis for the prediction of UTI exists, we used the data synthesized in the report by Hurlbut and Littenberg.18 Those authors identified and summarized 51 studies and generated summary receiver operating characteristic (ROC) curves for combinations of the nitrite and leukocyte esterase dipstick tests. They found that the nitrite-positive or leukocyte-esterase-positive combination had the greatest area under the ROC curve. The point on the summary ROC curve with the best accuracy represents a sensitivity of 75% and a specificity of 82%. With these values, the LR+ for a urinalysis is 4.2 and the LR– is 0.3 (Table 51-2). A range of similar points on the ROC curve that was supported by the largest number of studies was also examined, and the resulting LRs were similar in magnitude. Although other combinations of the nitrite and leukocyte esterase test will increase either sensitivity or specificity (eg, requiring both to be positive will decrease sensitivity and increase specificity), the nitrite- or leukocyte-esterase-positive combination was the most accurate test.18
Because the largest study to examine the accuracy of symptoms was also of lower quality,29 we performed a sensitivity analysis to determine the effect of this study on the summary LRs. Inclusion of this study always made the symptoms (dysuria, frequency, vaginal irritation, and vaginal discharge) appear to be more powerful diagnostic tests. However, in no case did inclusion of this study improve a test with marginal discriminatory power into the highly effective range (effectiveness score ≥ 3.0).24 The LR+ and LR– for dysuria and frequency excluded 1.0, whether or not the study was included, with one exception. The LR+ for increased urinary frequency was 1.8 (95% CI, 1.1-3.0) when all studies were included vs 1.4 (95% CI, 1.0-1.9) when the study was excluded. That study29 has a larger effect on the diagnostic value of vaginal symptoms because fewer studies were involved. The absence of vaginal discharge, a feature reported in only 3 studies, makes a UTI more likely whether or not this study29 is included (LR, 3.1 [95% CI, 1.0-9.3] for all studies vs LR, 1.7 [95% CI, 1.3-2.2] when excluded). The presence of vaginal discharge still decreases the likelihood of a UTI whether or not the study by Komaroff et al29 is included (LR, 0.34 [95% CI, 0.14-0.86] for all studies vs LR, 0.60 [95% CI, 0.39-0.91] when the study is excluded).
Symptoms suggestive of UTI are common complaints of young women seeking urgent medical care. Although textbooks of clinical medicine15, 16, and 17 routinely mention many of the symptoms and signs of UTI, the overall accuracy of these symptoms and signs has not previously been critically and systematically evaluated. A clear understanding of the value of each of these diagnostic tests may enable physicians to make more informed decisions about the choice of specific tests and management options.
Rule Out Complicated Urinary Tract Infection
The initial step is to be certain that the patient does not have a complicated UTI as defined by the factors listed earlier (see “Definitions” section). The probability of UTI in patients with risk factors for a complicated infection is not known because these patients were not included in the studies identified by our search. Such patients may be at greater risk of treatment failure,10 and clinicians may want to consider early urine culture and empirical treatment as shown at the top of the proposed algorithm (Figure 51-1).
Proposed Algorithm for Evaluating Women With Symptoms of Acute Urinary Tract Infection
Abbreviation: UTI, urinary tract infection.
aIn women who have risk factors for sexually transmitted diseases, consider testing for chlamydia. The US Preventive Services Task Force recommends screening for chlamydia for all women aged 25 years or younger and women of any age with more than 1 sexual partner, a history of sexually transmitted disease, or inconsistent use of condoms.52
bFor a definition of complicated UTI, see the “Definitions” section of the text.
cThe only physical examination finding that increases the likelihood of UTI is costovertebral angle tenderness, and clinicians may consider not performing this test in patients with typical symptoms of acute uncomplicated UTI (as in telephone management).
Pretest Probability and the Diagnostic Value of Presenting to a Clinician
With a standard evidence-based technique,21 a clinical encounter begins with an estimation of the pretest probability of disease, followed by the application of 1 or more diagnostic tests to determine the posttest probability of disease. We consider the pretest probability of UTI to be equal to the prevalence observed in studies of asymptomatic bacteriuria, or approximately 5%.11, 12 In this review, 5 studies reported the prevalence of UTI in patients presenting with 1 or more symptoms of acute UTI, and the summary prevalence was 48% (95% CI, 41%-55%).
The probability of UTI changes substantially when a patient presents to a clinician, increasing from 5% (in historical controls without symptoms) to approximately 50% (in patients in the included studies who presented with 1 or more symptoms). This change in probability corresponds to an LR of 19, representing a powerful “diagnostic test.” Clinically, it is useful to know that patients who present with 1 or more symptoms of UTI have a high probability of infection. Because all of the studies included in this review evaluated the diagnostic value of symptoms and signs after patients presented to a clinician, the relevant pretest probability for these tests is 50%.
Although the pretest probability of UTI in the average patient who presents with 1 or more symptoms is approximately 50%, this varies considerably according to the individual's risk profile. There are 3 well-established risk factors for acute UTI in young women: recent sexual intercourse,3, 34, 35, 36, 37, and 38 use of spermicide (on condoms or with diaphragms) during sexual intercourse,3, 34, 35, and 36, 39, 40 and history of UTI.3, 36 Other risk factors, including a maternal history of UTI,34 a history of childhood onset of UTI,34 and the presence of bacterial vaginosis,41 also have been found to be associated with UTI. The presence of any of these risk factors increases the pretest probability of UTI and should be considered when evaluating patients. Unfortunately, the diagnostic power of these risk factors (sensitivity, specificity, or LRs) is not known, because the majority of studies assessing these risk factors used a case-control design or did not present sufficient data to calculate LRs.3, 4, 35, 36, 37, 38, 39, 42 Further research is needed to determine the diagnostic power of these risk factors so that the information can be used during the clinical encounter to estimate the pretest probability of disease.
Refining Probability With the Medical History and Physical Examination
In the included studies, all diagnostic tests were evaluated by their ability to change the already high (50%) probability of UTI in the study population. Because these patients initially presented with at least 1 symptom, some of the power of each symptom was already “used up” by the time the patient presented to a clinician (and the probability of UTI increased from 5% to 50%). In a sense, the diagnostic power of the symptom is being “used” twice. Initially, the presenting symptom (most commonly dysuria or frequency) caused the patient to present to a clinician and was at least partially responsible for raising the probability of UTI from 5% to 50%. Subsequently, the value of the presenting symptom and all other potentially relevant symptoms was assessed after presentation to a clinician.
It is therefore not surprising that most of the individual symptoms and signs have LRs relatively close to 1.0 and therefore do not have great additional diagnostic power after presentation. The main exception to this finding is the history of vaginal discharge or vaginal irritation, which reduces the probability of UTI.
One study found that back pain and costovertebral angle tenderness were useful for predicting the presence of UTI.32 This study was a retrospective chart review of patients who had a urine culture in an emergency department, and it is possible that back pain and costovertebral angle tenderness were predictive of upper UTI (pyelonephritis). However, because none of the included studies performed a gold standard test for upper UTI, we were unable to determine whether individual symptoms and signs were more predictive of upper vs lower UTI. Most patients with symptoms suggestive of UTI and features classically associated with upper UTI (back pain, fever) are evaluated and treated for presumed pyelonephritis (Figure 51-1), even though the diagnostic accuracy of these signs and symptoms for predicting upper UTI is not known. Because most patients in the included studies did not have back pain and fever, we believe that the other symptoms evaluated in our review are most useful for predicting lower UTI (cystitis).
In contrast to the value of individual tests, certain combinations of symptoms result in large changes in the probability of UTI and represent powerful diagnostic tests. The combination of dysuria and frequency without vaginal discharge or irritation corresponds to an LR of 25. Although the combined LRs were generated from only 1 study of lower quality,29 these LRs were similar to those found when multiplying the summary LRs for the individual symptoms, suggesting that they are reasonable estimates of the true diagnostic power of these combinations. In addition, another study43 that was excluded from our analysis (because it included an unknown number of asymptomatic patients) used the same combinations of symptoms and found similar positive predictive values and LRs.
Although evaluated in only 1 study,33 self-diagnosis appears to be a useful diagnostic test (LR, 4.0) in women with recurrent UTI. Because this study did not perform urine cultures for women with mild or no symptoms, there is some uncertainty in the LR estimates. Similarly, the study population consisted of mostly highly educated single white women, and it is not clear whether the results apply to other groups of women. Nonetheless, these findings suggest that women learn to recognize the symptoms of UTI and are able to accurately diagnose a new infection, a finding that deserves further study and may have important implications for treatment of this large group of patients.
Refining Probability Using Dipstick Urinalysis
Dipstick urinalysis alone is a moderately powerful diagnostic test (Table 51-2). If the dipstick is used alone, the posttest probabilities for women with symptoms of a UTI are 81% (positive result) and 23% (negative result).
A Diagnostic Algorithm for Evaluating Patients With Symptoms of Urinary Tract Infection
Figure 51-1 shows a proposed algorithm for evaluating patients with symptoms of UTI. Although the algorithm itself has not been prospectively studied, the recommendations are based on the posttest probabilities of UTI generated from the summary LRs in the current analysis (Table 51-2). In women with risk factors for a complicated UTI or with back pain, fever, or malaise (suggesting possible pyelonephritis), a urine culture with initial empirical treatment is recommended. If a woman reports a history of vaginal discharge, the posttest probability of UTI from this single historical item is reduced to 23%, and a pelvic examination to rule out a vaginal infection should be considered in addition to a dipstick urinalysis and urine culture.
The algorithm highlights the finding that the medical history and physical examination alone can substantially increase the posttest probability of UTI, effectively “ruling in” the diagnosis. Because the only physical examination finding that increases the probability of UTI is costovertebral angle tenderness, the physical examination may be omitted without a substantial loss of diagnostic power in patients without a history of vaginal discharge or irritation. With individual summary LRs, a patient with dysuria, frequency, and hematuria (but no back pain at this point in the algorithm) has a posttest probability of UTI of 81%; with the combined LR estimate of dysuria and frequency without vaginal discharge (LR, 25), the posttest probability of UTI is 96%. Given these high probabilities of UTI, clinicians should consider empirical treatment without urine culture or dipstick urinalysis.
Conversely, even mostly negative history responses, physical examination findings, and dipstick urinalysis results cannot reliably rule out the diagnosis of UTI in women without a history of vaginal discharge or irritation. For example, to generate the lowest possible posttest probability of disease, a woman must still present with at least 1 symptom. If she presents with frequency (LR, 1.8) with no dysuria (LR, 0.5) and no back pain (LR, 0.8) (the only 2 negative symptoms other than vaginal symptoms), a negative dipstick result (LR, 0.3), and no other positive symptoms, her posttest probability of disease is still 18%, which is considerably higher than the prevalence of asymptomatic bacteriuria in the population (5%). Although we do not address the optimum treatment of such patients, we believe that the relatively high probability of UTI (~20%) warrants a urine culture (Figure 51-1), an approach that has been supported by others.10 Clinicians may also want to consider performing a pelvic examination, especially in patients at high risk for sexually transmitted disease or if the urine culture result is negative and symptoms persist. As noted, it is theoretically possible to rule out UTI in women who present with vaginal discharge, in which the lowest possible posttest probability of disease is 6% (if they also have no dysuria, no back pain, a negative dipstick result, and no other positive symptoms). We recommend that clinicians consider obtaining a urine culture in patients with at least 1 urinary symptom and vaginal discharge because the posttest probability of disease will only rarely reach this lowest possible 6%.
If the medical history and physical examination are neither strongly positive nor negative, a positive dipstick result still results in a high posttest probability of disease (approximately 80%), and empirical therapy should again be considered without urine culture. In all of the scenarios in the algorithm, urine culture may be indicated, without regard to the posttest probabilities, if the patient has experienced recurrent infection and antibiotic resistance is suspected.
Older guidelines for the evaluation of patients with suspected UTI recommend urine culture in all patients, even in those found to have a high probability of UTI after the medical history and physical examination.29, 44 More recent reviews and management strategies suggest that a diagnosis of UTI can be established in women who present with typical symptoms and are found to have a positive dipstick or urinalysis result (without obtaining a urine culture).10, 45, 46, 47, and 48
Unlike these treatment recommendations, our proposed algorithm (Figure 51-1) suggests that, in selected patients with mostly positive symptoms, the probability of UTI is so high (~90%) that empirical treatment may be considered without dipstick testing or urinalysis. A similar strategy was recently evaluated in a randomized trial comparing management via telephone with office evaluation in 72 women with suspected UTI.49 The investigators found no difference in symptom scores or patient satisfaction with the 2 strategies. Previous studies examining the effect of symptom-based treatment of patients with suspected UTI (after a telephone call or office visit to a health care provider) have shown that empirical therapy decreases costs without increasing adverse outcomes.50, 51 However, the main purposes of the current algorithm are to define the posttest probabilities of disease from specific clinical scenarios and to allow clinicians to make informed testing and treatment decisions based on their clinical judgment. Further research is needed to determine clinical outcomes, costs, and patient satisfaction associated with different testing and treatment strategies for treating patients who present with specific constellations of symptoms of UTI.
In the first case, the woman has 2 symptoms of UTI (dysuria and frequency), has no vaginal discharge, and believes that her current symptoms are similar to those of previous episodes. These features all increase her probability of UTI, which is greater than 90%. Her sexual history does not suggest that she is at high risk for a sexually transmitted disease. With the algorithmic approach, the patient should be asked about risk factors for complicated infection, as well as symptoms classically associated with pyelonephritis (fever, back pain, nausea, vomiting). As has been shown, telephone evaluation and treatment of similar patients may be an appropriate strategy.49, 50 In this patient, a positive dipstick urinalysis result would further increase the probability of UTI, whereas a negative result would not rule out infection.
In the second case, the woman has 2 symptoms of UTI (dysuria and frequency), as well as vaginal discharge (which decreases the probability of UTI and increases the probability of vaginal infection). A pelvic examination does not suggest a specific diagnosis and the dipstick urinalysis result is negative. The posttest probability of UTI is approximately 20%, illustrating that even a negative physical examination result and dipstick test result are insufficient to rule out UTI in a patient with 1 or more symptoms. A urine culture will help determine the need for treatment, and cervical cultures are indicated to rule out chlamydia and gonorrhea and help determine the cause of her symptoms.
In a woman who presents with 1 or more symptoms of UTI, the probability of infection is high (approximately 50%). Four symptoms (dysuria, frequency, hematuria, and back pain) and 1 sign (costovertebral angle tenderness) increase the probability of UTI when present. Combinations of symptoms can substantially increase the likelihood of UTI, effectively ruling in the disease according to the medical history alone. Patients with recurrent infection may be able to accurately self-diagnose UTI.
In contrast, the medical history and physical examination cannot reliably rule out UTI in women who present with urinary symptoms. Although 4 symptoms (absence of dysuria, absence of back pain, and a history of vaginal discharge or vaginal irritation) and 1 sign (vaginal discharge) decrease the probability of UTI, even combinations of symptoms, signs, and a negative dipstick result rarely decrease the probability of UTI below 20%. A urine culture and pelvic examination should be considered in patients who present with some symptoms of UTI but with mostly negative history responses and physical examination findings.
Dipstick urinalysis, which is a simple and inexpensive test, is moderately powerful and should be considered in women with appropriate urinary tract symptoms. If the dipstick result is positive, the probability of UTI is high, especially when combined with other positive findings from the medical history and physical examination. If the dipstick result is negative, the probability of disease is still relatively high (23%) and a urine culture should be considered to rule out infection.
Care should be taken to identify women with vaginal discharge or vaginal symptoms. If either is present, a pelvic examination and cervical culture are indicated to rule out infection caused by chlamydia52 or gonorrhea, as well as other vaginal infections that require definitive therapy. Similarly, in women with back pain, fever, or significant malaise, an office examination, combined with dipstick urinalysis and urine culture, may aid in the diagnosis of pyelonephritis, although the accuracy of individual tests for establishing upper UTI is not known.
Knowledge of the LRs for specific symptoms, signs, and diagnostic tests used to evaluate patients with suspected UTI may improve the ability of clinicians to more accurately predict the probability of infection in individual patients. It seems reasonable to offer empirical treatment when the probability of infection is high and to pursue additional diagnostic testing (eg, urine culture, pelvic examination, and cervical cultures) when the probability of UTI is low or intermediate. However, the actual cost-effectiveness of specific testing and treatment strategies is not clearly established, and prospective studies examining clinical benefits, adverse effects, costs, and patient satisfaction with specific approaches are needed.
Author Affiliations at the Time of the Original Publication
University of California, San Francisco, and General Internal Medicine Section, San Francisco Veterans Affairs Medical Center, San Francisco (Dr Bent); Department of Medicine, University of Michigan Medical School, Ann Arbor (Dr Nallamothu); Department of Medicine, Durham Veterans Affairs Medical Center and Duke University School of Medicine, Durham, North Carolina (Dr Simel); Health Services Research and Development Center of Excellence, Veterans Affairs Puget Sound Health Care System, Seattle, Washington (Dr Fihn); and Department of Medicine, Ann Arbor Veterans Affairs Medical Center and Patient Safety Enhancement Program, University of Michigan Health System, Ann Arbor (Dr Saint).
We thank Lori Bastian, MD, PhD, Michael Hayden, MD, Kathleen Klink, MD, and Joanne Piscitelli, MD, for their thoughtful comments on an earlier version of this work.
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