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Research ArticleOriginal ResearchA

Toward A Simple Diagnostic Index for Acute Uncomplicated Urinary Tract Infections

Bart J. Knottnerus, Suzanne E. Geerlings, Eric P. Moll van Charante and Gerben ter Riet
The Annals of Family Medicine September 2013, 11 (5) 442-451; DOI: https://doi.org/10.1370/afm.1513
Bart J. Knottnerus
1Department of General Practice, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
MD, PhD
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  • For correspondence: b.j.knottnerus@amc.uva.nl
Suzanne E. Geerlings
2Department of Internal Medicine/Infectious Diseases, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
MD, PhD
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Eric P. Moll van Charante
1Department of General Practice, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
MD, PhD
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Gerben ter Riet
1Department of General Practice, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
MD, PhD
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Article Figures & Data

Figures

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  • Figure 1
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    Figure 1

    Discrimination by subsequent tests when performed for all patients.

    UTI=urinary tract infection.

    Notes: In the boxes, patient numbers in each predicted risk category (with corresponding percentage in brackets) are shown after application of each subsequent diagnostic model to all 196 patients. The predicted risk categories used are <30%, 30%–70% and >70%. The vertical arrows display the numbers of patients that switch between categories after performing a test. The observed risks (and their 95% CIs) are shown in italics.

    The figure is best read from left to right: 196 patients (100%) were included and the prevalence of UTI was 61%. Based on the results from the history questions only, 28 patients (14%) had a predicted risk of <30% and 81 patients (41%) had a predicted risk of >70%. When both history and a urine dipstick were performed, 68 patients (35%) had a predicted risk of <30% and 76 patients (39%) had a predicted risk of >70%. Additional performance of a sediment and dipslide resulted in removal from the intermediate category of 20 more patients (11%), mainly those who were correctly classified into the highest risk category after history only, but were incorrectly reclassified into the intermediate risk category after a negative nitrite test result on a urine dipstick. All observed risks were close to the predicted risks (good calibration).

  • Figure 2
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    Figure 2
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    Figure 2

    Discrimination by subsequent tests when performed in patients in the intermediate risk category only.

    UTI=urinary tract infection.

    Notes: In the boxes, patient numbers (percent) in each predicted risk category are shown after application of each subsequent diagnostic model to patients in the intermediate predicted risk category only for the scenarios history + dipstick + sediment and history + dipstick + dipslide (Figure 2A and 2B, respectively). The predicted risk categories used are <30%, 30%–70% and >70%. The vertical arrows display the numbers of patients that moved from the intermediate risk category to one of the extreme risk categories (<30% or >70%) after performing a test. The observed risks (95% CI) are in italics.

    Figures are best read from left to right: 196 patients (100%) were included, and the prevalence of UTI was 61%. Based on the results from the history questions only, 28 patients (14%) had a predicted risk of <30% and 81 patients (41%) had a predicted risk of >70%. After subsequent performance of a urine dipstick for patients in the intermediate risk category, 62 patients (32%) had a predicted risk of <30%, 100 patients (51%) had a predicted risk of >70%, and 34 patients (17%) remained in the intermediate risk category (between 30% and 70%) as the result of a negative nitrite test and a positive blood test. Subsequent performance of either a sediment or a dipslide reclassified 5% or 7%, respectively, of patients from the intermediate category into the high-risk category (>70%) because of a positive test result (Figure 2A and 2B, respectively). All observed risks were close to the predicted risks (good calibration).

Tables

  • Figures
  • Additional Files
    • View popup
    Table 1

    Distribution of Patient Characteristics: History

    CharacteristicNo. (% of Total)Culture Sample, No.Positive Culture %
    PositiveNegative
    Total196 (100)1207661
    Ethnicity
     Dutch/German171 (87)1076463
     Surinam/Antillian/Aruban15 (8)6940
     Other10 (5)7370
    General health
     Very good22 (11)121055
     Good110 (56)743667
     Reasonable44 (22)251957
     Moderate11 (6)7464
     Bad9 (5)2722
    Marital status
     Married81 (41)513063
     Partner, cohabitating31 (16)201165
     Partner, living apart36 (18)241267
     Single48 (24)252352
    ≥ First-grade relative with recurrent UTIs?
     No137 (70)835461
     Yes59 (30)372263
    Last menstruation >1 year ago?
     No133 (68)815261
     Yes63 (32)392462
    Diabetes mellitus according to patient?
     No172 (88)1116165
     Yes24 (12)91538
    Times of sexual activity in past week
     067 (34)343351
     139 (20)231659
     240 (21)33783
     322 (11)14864
     414 (7)9564
     ≥514 (7)7750
    UTIs in past year according to patient
     092 (47)573562
     128 (14)24486
     230 (15)191163
     ≥332 (16)151747
     Don’t know14 (7)5936
    ≥1 UTI ever diagnosed according to patient?
     No42 (21)241857
     Yes154 (79)1005465
    Patient thinks she has a UTI?
     No9 (5)4544
     Yes164 (84)1145070
     Don’t know23 (12)2219
    Symptoms
    Duration of symptoms, d
     018 (9)12667
     140 (20)281270
     237 (19)231462
     337 (19)221559
     424 (12)141058
     ≥540 (20)211953
    False urge to urinate
     No54 (28)302457
     A little82 (42)532965
     Quite much43 (22)271663
     Very much17 (9)10759
    More frequent micturition than usual
     No12 (6)3925
     A little62 (32)313150
     Quite much81 (42)592273
     Very much41 (21)271466
    Pain during micturition
     No35 (18)142239
     A little73 (37)393453
     Quite much64 (33)531183
     Very much23 (12)14961
    Urge to urinate hard to control
     No49 (25)222745
     A little88 (45)573165
     Quite much33 (17)24973
     Very much26 (13)17965
    Vaginal discharge
     No133 (68)864765
     A little49 (25)272255
     Quite much14 (7)7750
     Very much0 (0)00n/a
    Vaginal irritation or itching
     No110 (56)723865
     A little57 (29)282949
     Quite much19 (10)15479
     Very much10 (5)5550
    Bother at work/school
     No24 (13)91538
     Hardly37 (19)211657
     Moderate69 (35)482170
     Much46 (23)291763
     Very much20 (10)13765
    Bother at social activities
     No47 (24)242351
     Hardly49 (25)292059
     Moderate53 (27)361768
     Much33 (17)211264
     Very much14 (7)10471
    • n/a=not applicable; UTI=urinary tract infection.

    • a Percentages represent the fraction of positive cultures for the corresponding characteristic, eg, 70% of patients with symptoms for 1 day had a positive culture (implying that the positive predictive value of having symptoms for 1 day is 70%).

    • View popup
    Table 2

    Univariate Distributions of Patient Characteristics: Urinalysis

    CharacteristicNo. (% of Total)Culture Result, No.Positive Culture, %a
    PositiveNegative
    Total196 (100)1207661
    Dipstick
    Blood
     Negative35 (18)112431
     Trace38 (20)152339
     1+29 (14)20969
     2+36 (19)261072
     3+58 (30)481082
    Leukocytes
     Negative39 (20)102926
     Trace15 (8)51033
     1+47 (24)311666
     2+35 (18)27877
     3+60 (31)471378
    Nitrate positive
     No133 (68)607345
     Yes62 (32)60395
    Sediment
    Bacteria, No./HPF
     None52 (27)183435
     Few48 (24)271756
     Many53 (27)401375
     Very many43 (22)35881
    Leukocytes, No./HPF
     026 (13)62023
     1–332 (16)92328
     4–1018 (9)9950
     11–2024 (12)141058
     ≥2096 (49)821485
    Dipslide
    CLED medium, CFU/mL
     <10364 (33)214333
     103–10432 (16)102231
     104–10510 (5)6460
     ≥10590 (46)83792
    • CFU = colony-forming unit; CLED = cystine lactose electrolyte deficient; HPF = high-power field.

    • ↵a Percentages represent the fraction of positive cultures for the corresponding characteristic.

    • View popup
    Table 3

    Clinical Scores for History Only and History + Dipstick: Regression Coefficients and Scores of Selected Indicators

    IndicatoraHistory OnlyHistory+Dipstick
    Odds Ratio (95% CI)CoefficientScoreOdds Ratio (95% CI)CoefficientScore
    History
     Patient thinks she has a UTI8.85 (3.35–24.05)2.18815.64 (3.94–63.43)2.7511
     At least considerable pain on micturition2.80 (1.52–5.16)1.0340.97 (0.91–1.03)−0.030b
     Vaginal irritationc0.77 (0.54–1.08)−0.26−10.61 (0.36–1.04)−0.50−2
    Dipstick
     Nitrate positive–––31.19 (7.39–130.32)3.4414
     Blood ≥1+–––7.32 (3.03–17.81)1.998
     Regression intercept–−1.77––−3.89–
    • UTI=urinary tract infection.

    • ↵a Indicators from history and urine dipstick that were retained after logistic regression analysis with bootstrapped backward elimination (P remove .05).

    • ↵b This clinical score of 0 had no added value.

    • ↵c Vaginal irritation reduced the probability of a positive culture, whereas the other indicators increased it.

    • View popup
    Table 4

    Clinical Scores for History Only, and History + Dipstick: Sum Scores and Predicted Probabilities per Risk Category

    Risk CategoryHistory OnlyHistory+Dipstick
    ScorePredicted Probability (95% CI)ScorePredicted Probability (95% CI)
    <30%≤316 (7–34)≤1215 (7–31)
    30%–70%4–856 (44–68)14–1761 (41–77)
    >70%≥1179 (69–86)≥1991 (76–96)
    • Notes: For example, for history only, patients with a sum score of ≥3 have a predicted probability of 16% and are therefore classified into the lowest risk category (<30%).

Additional Files

  • Figures
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  • Supplemental Appendix

    Supplemental Appendix. Detailed Description of Variable Selection Method

    Files in this Data Supplement:

    • Supplemental data: Appendix - PDF file, 2 pages
  • The Article in Brief

    Toward a Simple Diagnostic Index for Acute Uncomplicated Urinary Tract Infections

    Bart J. Knottnerus , and colleagues

    Background Sixty percent of all women experience at least one acute uncomplicated urinary tract infection (UTI) during their life. Various medical history questions and urine investigations can be used for UTI diagnosis. This study analyzes different approaches to diagnosing acute uncomplicated urinary tract infections in women and proposes a model that reduces the number of questions asked and urine investigations needed.

    What This Study Found Analyzing data on 196 women presenting with painful and/or frequent urination, researchers find that 3 questions, sometimes followed by a urine dipstick test, can provide a practical level of accuracy. Specifically, they recommend asking (1) does the patient think she has a UTI, (2) is there at least considerable pain on urination and (3) is there vaginal irritation? Asking these questions, they find, may be sufficient to correctly classify more than one-half of women with painful and/or frequent urination as having UTI risk of either less than 30 percent or greater than 70 percent. Subsequent performance of nitrite and blood dipstick tests raises this proportion to 73 percent. The percentage rises to 83 percent if a urine dipstick is performed only for patients with a UTI risk between 30 percent and 70 percent after history and avoids the possibility of a false-negative nitrate tests in patients with high UTI risk (greater than 70 percent) after history.

    Implications

    • Expensive and time-consuming urinary sediment and dipslide tests may add little diagnostic information. The authors call for future research to validate these recommendations.
  • Annals Journal Club

    Sep/Oct 2013: Diagnosing Urinary Tract Infections


    The Annals of Family Medicine encourages readers to develop a learning community of those seeking to improve health care and health through enhanced primary care. You can participate by conducting a RADICAL journal club and sharing the results of your discussions in the Annals online discussion for the featured articles. RADICAL is an acronym for Read, Ask, Discuss, Inquire, Collaborate, Act, and Learn. The word radical also indicates the need to engage diverse participants in thinking critically about important issues affecting primary care and then acting on those discussions.1

    HOW IT WORKS

    In each issue, the Annals selects an article or articles and provides discussion tips and questions. We encourage you to take a RADICAL approach to these materials and to post a summary of your conversation in our online discussion. (Open the article online and click on "TRACK Comments: Submit a response.") You can find discussion questions and more information online at: http://www.AnnFamMed.org/site/AJC/.

    CURRENT SELECTION

    Article for Discussion

    • Knottnerus BJ, Geerlings SE, Moll van Charante EP, ter Riet G. Toward a simple diagnostic index for acute uncomplicated urinary tract infections. Ann Fam Med. 2013;11(5):442-451.

    Discussion Tips

    Urinary tract infections are common, and clinicians' diagnostic approaches are based on long tradition, local practice, and personal experience. This interesting clinical study provides empirical information on the conjoint diagnostic value of combinations of medical history and simple laboratory testing for acute uncomplicated urinary tract infections in women with painful and/or frequent urination.

    Discussion Questions

    • What question is asked by this study, and why does it matter?
    • How does this study advance beyond previous research and clinical practice on this topic?
    • How strong is the study design for answering the question?
    • To what degree can the findings be accounted for by:
      1. How patients were selected, excluded, or lost to follow-up?
      2. How the main variables were measured?
      3. Confounding (false attribution of causality because 2 variables discovered to be associated actually are associated with a 3rd factor)?
      4. Chance?
      5. How the findings were interpreted?
    • What do you think of the outcome variable?
    • How comparable is the study sample to similar patients in your practice? What is your judgment about the transportability of the findings?
    • What are the main study findings?
    • Which approach indicated by the different models do you think you are likely to use, and how might your approach vary based on patient characteristics?
    • Do you think the findings have implications for self-treatment by selected patients?
    • What are the next steps in interpreting or applying the findings?
    • What researchable questions remain?

    References

    1. Stange KC, Miller WL, McLellan LA, et al. Annals Journal Club: It's time to get RADICAL. Ann Fam Med. 2006;4(3):196-197.

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Toward A Simple Diagnostic Index for Acute Uncomplicated Urinary Tract Infections
Bart J. Knottnerus, Suzanne E. Geerlings, Eric P. Moll van Charante, Gerben ter Riet
The Annals of Family Medicine Sep 2013, 11 (5) 442-451; DOI: 10.1370/afm.1513

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Toward A Simple Diagnostic Index for Acute Uncomplicated Urinary Tract Infections
Bart J. Knottnerus, Suzanne E. Geerlings, Eric P. Moll van Charante, Gerben ter Riet
The Annals of Family Medicine Sep 2013, 11 (5) 442-451; DOI: 10.1370/afm.1513
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