Family Practice Vol. 20, No. 2, 103-107
© Oxford University Press 2003
Clinical Research |
What is the predictive value of urinary symptoms for diagnosing urinary tract infection in women?
a EAP, Mallorca, IB-Salut,
b EAP, Menorca, IB-Salut,
c EAP, Eivissa-Formentera, IB-Salut and
d Gerència d’Atenció Primària de Mallorca.
Correspondence to David Medina i Bombardó, Unitat d’Investigació de la Gerència d’Atenció Primària de Mallorca, IB-Salut, Carrer de Reina Esclaramunda 9, 07001 Palma, Spain; E-mail: dbombardo{at}terra.es
Medina-Bombardó D, Seguí-Díaz M, Roca-Fusalba C, Llobera J and the dysuria team. What is the predictive value of urinary symptoms for diagnosing urinary tract infection in women? Family Practice 2003; 20: 103–107.
Received 23 April 2002; Revised 18 September 2002; Accepted 4 November 2002.
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Abstract |
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Objectives. Our aim was to determine the probability of correctly diagnosing urinary tract infections (UTIs) from urinary symptoms and signs, studying their sensitivity, specificity and likelihood ratio (LR) when clinical history, signs and reactive strip test results are taken into account.
Methods. An epidemiological analysis with a diagnostic and clinical orientation was carried out in a primary health care setting. The subjects comprised 343 women 
14 years of age who consulted their family physician for incident urinary tract symptoms. A guided medical examination was carried out using a check-list formulary, reactive strip test, urine culture and the clinical course of all patients.
Results. The pre-test probability of having UTI among patients with incident urinary symptoms is 0.484 [95% confidence interval (CI) 0.431–0.536]. Positive LRs for UTI are: painful voiding 1.31 (95% CI 1.12–1.54), urgency 1.29 (95% CI 1.12–1.50), urinary frequency 1.16 (95% CI 1.06–1.28) and tenesmus 1.16 (95% CI 1.02–1.32). The probability of UTI is reduced by the presence of genital discomfort, dyspareunia, vaginal discharge, positive lumbar fist percussion and perineal discomfort. Nitrites on the urine reactive strip test increase the probability of UTI by >5 times, moderate pyuria increases it by >1.5 times, and the presence of both findings does so by >7 times.
Conclusions. In women with urinary symptoms, a thorough clinical examination, together with performance of a reactive strip test during the office visit, improves the chances of detecting UTI.
Keywords. Diagnostic test, dysuria, likelihood ratio, predictive value, primary health care, urinary tract infection.
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Introduction |
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Urinary tract infections (UTIs) have been studied extensively from microbiological and therapeutic perspectives, but there are few publications dealing with their clinical epidemiology, particularly in primary health care (PHC), the setting where they are seen most often.1–3 Urinary symptoms are the eighth most common presenting complaint in PHC, afflicting one out of every 5161 of our patients. While up to 90% of patients with UTI complain of urinary tract symptoms, one-third or more of patients with these symptoms do not have bacteriuria.1 Faced with a patient who consults for urinary symptoms, family physicians must make relevant clinical and therapeutic decisions before the diagnosis of UTI can be confirmed.
Therefore, our aim was to determine the true value of the routine clinical work-up of patients presenting with urinary symptoms, by determining the likelihood of diagnosing a UTI based on the results of clinical history and physical examination, and how such a likelihood can vary when clinical data are seen in light of the results of the reactive strip test.
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Methods |
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We studied women
14 years of age from urban and suburban areas of the Balearic Islands (Spain) who consulted a physician with incident urinary symptoms. We defined ‘urinary symptoms’ as the presence of one or more of the following: painful voiding, frequency, urgency, difficulty, burning, tenesmus, and diurnal and/or nocturnal urinary incontinence.
Symptoms were incident when the problem or episode was new and had not led the patient to consult a physician or to initiate any form of treatment. We took urinary tract symptoms to be the presenting complaint when the patient spontaneously described the symptoms or if the physician suspected the possibility of UTI during the clinical interview. We excluded all episodes already treated by a physician or by the patient herself, within the previous 15 days. Sample size was calculated in 384 women (probability of UTI p = q = 0.5, 
0.05, ß 0.20 and 5% precision). Allowing for 10% losses, our sample size was 426 women.
The 35 physicians from 18 PHC centres who participated in the study received instructions on data collection. All patients meeting the inclusion criteria were submitted to a guided medical exam (clinical interview and physical examination, using a check-list formulary with specific questions and yes/no answers for every item identified in Tables 1 and 2
) and to a routine urine test as well as an in situ urine reactive strip test. Systematically and independently of clinical results, and before starting any treatment, another urine sample was sent for culture to the reference laboratory, by the usual route. The reactive strip test was done and read by the physician or a nurse; no specific instructions were given for this test in order to keep the study conditions as close as possible to routine practice. Nurses and laboratory personnel were blinded to the clinical data. A second clinical evaluation was done when the culture result was received.
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Clinical history, symptoms, signs, in situ urinary strip test and urine culture results were used to calculate the sensitivity, specificity, likelihood ratios (LRs) and 95% confidence intervals (95% CIs) of urinary symptoms with respect to a positive culture result. The cut-off value of the reactive strip, calculated for our sample by the ROC curve for all possible values, was
70 leukocytes/ml (small in Ames Multistix®); for agar culture, the cut-off was the routine one for the reference laboratory (100 000 c.f.u./µl of common pathogens). Data analyses were performed with SPSS 8.0, and Microsoft-Excel 7.0 was used to calculate LRs and their 95% CIs. |
Results |
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We included 417 women, of whom 414 had urine cultures taken (three declined to participate). Another 34 women were lost to follow-up, while the culture was felt to be contaminated in 37 cases, so that 343 cases (89% of the number foreseen) were taken as valid for a positive or negative urine culture. The median age was 44 years (range 15–90), and two modes were observed, one having a broad base comprising young women of reproductive age (14–45 years), and the other group ranging in age from 65 to 75. There were no significant differences in age between women with a positive, negative or contaminated culture, or those lost to follow-up. Cultures were positive in 166 cases (39.8% of all women) and negative in 177 (42.4%), giving a pre-test probability of having a UTI among women with incident urinary symptoms of 0.484 (95% CI 0.431–0.536). Relative frequency, sensitivity, specificity, positive and negative LR values of studied variables are given in Tables 1 and 2
. None of the more common symptoms (frequency, burning, tenesmus, urgency and painful voiding) had a specificity for UTI of >50%. Any symptom associated with urgency is more likely to be related to UTI. The absence of urgency together with the absence of any one of the other symptoms makes UTI less likely.
We identified no item in the patient’s history nor any accompanying sign or symptom that increases the likelihood of UTI. In fact, a history of urolithiasis or vaginitis, a positive fist percussion, perineal, genital or lower abdominal discomfort, vaginal discharge or dyspareunia decrease the likelihood of a diagnosis of UTI.
Overall, the findings most strongly correlated with UTI are a positive nitrite test and pyuria, in that order. The co-existence of both findings increases the probability of UTI by >7 times.
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Discussion |
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We have found other studies in the literature with a similar perspective to ours.2–7 In most instances, there is no definition of the clinical terminology employed, so that it is difficult to compare the results of different studies. For example, there is no uniform definition of ‘dysuria’, the term employed most frequently in the context of urinary problems.1,3,7,9
It must be borne in mind that our study population is not representative of the general population, but of women who consulted a PHC facility for some type of urinary symptom (90.7%) or for some type of problem which the health professional believed might be related to the urinary tract (9.3%). The 48.4% prevalence of UTI in our population differs from that found in other studies.1–4,6–8 This difference in prevalence can probably be explained as the result of different inclusion criteria, different levels of the cut-off value for considering a urine culture positive, and the characteristics of the study population (age or setting). The predictive value of different symptoms likewise can vary depending largely on their definition, the examining clinician and the way in which the patient describes her symptoms. In the literature, we found a significant LR for ‘dysuria’,5,7 but the term was not well defined.
In the presence of new urinary symptoms, in our series, a history of urolithiasis decreases the probability of UTI, and a history of previous UTI is not a predictive factor for diagnosing a new episode, a result that is surprising but similar to that found by others.2 A positive lumbar fist percussion, which is often found in cases of upper UTI, whether because of the difficulty of getting different researchers to apply a standard technique for evoking this sign, or because it really does have a low predictive value, this sign clearly reduces the likelihood of UTI in our series, while it improves it in others.5
The power of our study was low for cases of pregnancy (1.2%), malformations of the urinary tract (2.6%), a history of sexually transmitted diseases (1.7%), diaphragm use (1.2%), genital ulcers (0.5%) and vaginal discharge (2.4%).
In our study, the urine reactive strip test in patients in which UTI was considered likely on clinical grounds has been highly useful for increasing the likelihood of detecting UTI. This finding is similar to that seen by other authors.4,6,10
The search for a predictive model for diagnosing UTI was intended to provide a useful tool for physicians in clinical practice, where diagnostic tools are scarce. Our study suggests that the evaluation of clinical signs and symptoms together with the results of pyuria and nitrituria in the reactive strip test may help the PHC physician to make relevant decisions before UTI is confirmed by the results of culture.
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Acknowledgments |
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We thank Francisco Campoamor MD, for his thoughtful comments on an earlier version of this work. Funding for this study was from the Fondo de Investigaciones Sanitarias (FIS) [Health Research Fund] reference number 96/0024-00, in order that the work form part of a doctoral thesis to the Universitat Autònoma de Barcelona.
Members of the dysuria team: V Thomàs-Mulet, A Jover-Palmer, J González-Garcia, J Ochogavia-Cànaves, F Fiol-Gelabert, J Miquel-Gomàra, A Daviu-Pastor, M Bestard-Serra, S Pizarro-Anglada, RM Francisco-Soms, M Sauleda-Parés (Family Physicians, EAP, Mallorca, IB-Salut), A Estela-Mantola, MP Juan-Pérez, A Castelló-Sabater, JM Gardeñes-Morón, A González-Martin (Family Physicians, EAP, Menorca, IB-Salut), O Gassent-Sanchís, JJ Lalanza-Laseras, G Navarro-Aznárez, M Tresserra-Suab, ML Plana-Garcia (Family Physicians, EAP, Eivissa-Formentera, IB-Salut), E Fuentespina-Vidal, P Sastre-Alzamora (Laboratori del Carme, Son Dureta Hospital, IB-Salut), D Balsells-Rosselló (Can Misses Hospital, Eivissa, IB-Salut), C Rodríguez-Moreno (SERGAS), V Riera-Marí (Son Dureta Hospital, IB-Salut).
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References |
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