Which women with stress incontinence require urodynamic evaluation?

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1 Which women with stress incontinence require urodynamic evaluation? Alison C. Weidner, MD, Evan R. Myers, MD, MPH, Anthony G. Visco, MD, Geoffrey W. Cundiff, MD, and Richard C. Bump, MD Durham, North Carolina OBJECTIVE: This study was undertaken to determine the predictive value of the symptom of stress urinary incontinence and to evaluate the ability of other factors suggested by a published Agency for Health Care Policy and Research guideline for the discrimination of patients unlikely to require urodynamic testing before surgical management. STUDY DESIGN: We evaluated 950 consecutive women without advanced (stage III or IV) pelvic organ prolapse who were referred with symptoms of incontinence. Incontinence was recorded by means of standard forms and was characterized as any stress loss (76.4%), primarily stress loss (58.9%), stress loss only (29.8%), stress and urge loss (52.2%), urge loss only (13.8%), constant and stress loss (1.9%), or constant loss (2.3%). Other variables were assessed by means of a standardized history, physical examination (including urethral axis determination and stress test), 1-week urinary diary, and postvoid residual volume measurement. A urodynamic diagnosis of pure genuine stress incontinence was used as the criterion standard. Sensitivity, specificity, and positive and negative predictive values were calculated. Logistic regression models incorporating various combinations of stress loss only, previous prolapse or incontinence surgery, nocturia, voiding frequency, urethral hypermobility, and postvoid residual volume <100 ml (the factors recommended by the Agency for Health Care Policy and Research guidelines), along with age and race as predictors of genuine stress incontinence, were constructed to evaluate the predictive ability of the guideline in a subset of 447 patients for whom data on all variables were available. RESULTS: Of the entire population 480 (50.5%) had pure genuine stress incontinence, 134 (14.1%) had both genuine stress incontinence and detrusor instability, 180 (18.9%) had pure detrusor instability, and 40 (4.2%) had intrinsic sphincter deficiency. Fifty-four (5.7%) had normal study results, and 62 (6.5%) had other nonincontinence diagnoses. Among the subjects with symptoms of stress loss only, 10.8% did not have genuine stress incontinence confirmed on urodynamic examination. Agency for Health Care Policy and Research guideline criteria had excellent discrimination (C statistic of 0.807) compared with the sole criterion of stress urinary incontinence only (C statistic of 0.574), with a positive predictive value of 85.7%. Only 7.8% of subjects met all the criteria, however, and 5.7% of these ultimately had a urodynamic diagnosis of either detrusor instability or normal study result. CONCLUSION: The predictive value of stress symptoms alone was not high enough to serve as the basis for surgical management. Agency for Health Care Policy and Research guidelines improved the predictive value but were applicable to only a small subset of patients referred with urinary incontinence. (Am J Obstet Gynecol 2001;184:20-7.) Key words: Genuine stress incontinence, logistic modeling, receiver operating characteristic curve, urinary incontinence Multiple studies in the recent literature have attempted to identify reliable and inexpensive evaluation methods for women with urinary incontinence. 1-4 Several studies have shown that subjective symptoms alone are From the Division of Gynecologic Specialties, Department of Obstetrics and Gynecology, Duke University Medical Center. Received for publication November 10, 1999; revised January 20, 2000; accepted March 25, Reprint requests: Alison C. Weidner, MD, Assistant Professor, Division of Gynecologic Specialties, Department of Obstetrics and Gynecology, Box 3192, Duke University Medical Center, Durham, NC Copyright 2001 by Mosby, Inc /2001 $ /1/ doi: /mob not predictive of diagnosis 3-5 and have recommended specialized testing procedures before initiation of therapy. 6, 7 This usually means referral for multichannel urodynamic studies, which are not universally available, are expensive to perform, and are not perfectly reproducible. 8 Furthermore, because the lifetime risk of undergoing surgery for urinary incontinence in the United States is estimated at 11.1%, 9 the population undergoing surgical repair far outstrips the capacity of available urodynamic facilities. This means that some patients with incontinence undergo surgery on the basis of symptoms and physical examination alone. Clinical practice guidelines published by the Agency for Health Care Policy and 20

2 Volume 184, Number 2 Weidner et al 21 Research (AHCPR) recommended considering surgery without referral for urodynamic testing for patients with symptoms of pure stress urinary loss and a voiding history and results of physical examination suggestive of pure hypermobility genuine stress incontinence 10 that includes the following: Urine loss occurs only with physical exertion (history and stress test). Voiding habits are normal ( 8 episodes per day and 2 episodes per night). There are no neurologic history and no neurologic findings. Patient has no history of anti-incontinence or radical pelvic surgery. Pelvic examination documents hypermobility of the urethra and bladder neck, pliable and compliant vaginal wall, and adequate vaginal capacity. Postvoid residual volume is normal. Patient is not pregnant. A 1996 update published by the AHCPR made essentially no changes to these criteria. 11 Unfortunately, few women are seen with pure symptoms of either stressassociated or urge-associated urinary loss, with as many as 30% to 50% of women reporting symptoms of both stress and urge incontinence. 3, 5 Some women who report pure stress or urge symptoms ultimately have a condition at odds with the reported symptoms diagnosed at urodynamic examination, with no absolutely reliable clinical predictors identified for either pure genuine stress incontinence or pure detrusor instability. 3-5 The accuracy of a prediction of genuine stress incontinence is improved by using a combination of strict historical and clinical parameters, but a proportion of such women will still have detrusor instability alone or genuine stress incontinence and detrusor instability. 1 Ethnic comparison studies suggest that race is an important parameter, because the prevalence of genuine stress incontinence among white women may be as much as 2.3 times that among African American women. 12 The age of the patient is also potentially important, because detrusor instability is significantly more common among older women than among younger women. 13 The objectives of this study were (1) to evaluate the sensitivity and specificity of urinary incontinence symptoms for the diagnosis of genuine stress incontinence and (2) to evaluate the clinical discrimination of the AHCPR criteria in a large population of patients with urinary incontinence. We wished to characterize a group of women for whom multichannel urodynamic studies are not necessary before surgical treatment, with the AHCPR criteria as one standard. We also wanted to determine whether any patients who met the AHCPR criteria actually had a urodynamically confirmed condition that was inappropriate for surgery. To accomplish these objectives we assessed the sensitivity, specificity, and positive and negative predictive values of various combinations of symptoms of stress and urge incontinence for a urodynamic diagnosis of pure genuine stress incontinence. We similarly assessed the discrimination of the AHCPR criteria for the diagnosis of genuine stress incontinence. We then analyzed other historical and physical examination data in an effort to identify other findings that might improve the discrimination of the criteria. Methods Data on 1406 consecutive patients referred for multichannel urodynamic testing were examined. Women with stage III or IV pelvic organ prolapse, women with no reports of urinary incontinence, and women undergoing repeat examinations were excluded. This retrospective analysis therefore included the records of 950 women with urinary incontinence during a 10-year period from 1988 to A total of 535 of these women were included in a previous report of clinical predictors of pure genuine stress incontinence and pure detrusor instability. 5 Evaluations took place at the Medical College of Virginia (n = 242) or Duke University Medical Center (n = 708). All subjects had negative results of urine culture before urodynamic evaluation and were not pregnant. We used a standardized approach that included a uniform history, physical examination (including urethral axis determination and stress test), 1-week validated urinary diary, 14 pad quantitation testing, postvoid residual volume, and multichannel urodynamic studies as described previously elsewhere. 5, 15 The diagnosis of genuine stress incontinence was made if the subject had the symptom of stress incontinence and had observable leakage produced by stress without concurrently demonstrable detrusor activity during urethrocystometry or urethral profilometry or had a positive result of a direct visualization test immediately after the catheters were removed in the total absence of detrusor instability during previous urethrocystometry. The diagnosis of detrusor instability was made if the subject had a detrusor contraction in association with urgency and leakage. The diagnosis of intrinsic sphincteric deficiency was made on the basis of combined historical, physical, urodynamic, and endoscopic parameters. 16, 17 All diagnoses determined at urodynamic examination were made according to standard International Continence Society definitions. 18 A patient with no genuine stress incontinence, detrusor instability, or intrinsic sphincteric deficiency or with other nonincontinence diagnosis was considered to have a normal study result. Other nonincontinence diagnoses included emptying phase dysfunction or pelvic organ prolapse, with standard definitions. 19 We categorized the reported incontinence symptoms as any stress loss, stress loss only, stress and urge loss, urge loss only, stress and constant loss (constant wetness with stress-associated spurts of urine), and constant

3 22 Weidner et al January 2001 Table I. Characteristics of patient population Patients in regression analysis (n = 447) All patients (n = 950) Age (y, mean ± SD) 54.8 ± ± 13.9 Parity (median and range) 2 (0-5) 2 (0-12) Weight (kg, mean ± SD) 75 ± ± 19 Race (%) White 88.1% 86.5% African American 11.0% 12.6% Hispanic 0.7% 0.4% Other 0.2% 0.5% Previous hysterectomy (%) 60.9% 57.5% Previous prolapse or incontinence surgery (%) 37.4% 35.5% Stage of prolapse (%) Stage 0 8.1% 8.9% Stage I 28.4% 28.4% Stage II 63.5% 62.7% Enuresis (%) 7.4% 11.7% Incontinent episodes/wk (mean ± SD) 25 ± ± 116. Diurnal frequency (h, mean ± SD) 2.3 ± ± 1.1 Nocturic episodes/wk (mean ± SD) 6.3 ± ± 10. loss (reports of being always wet). A description of primarily stress loss was further assigned to those patients who reported stress urinary loss to be the most significant symptom. These symptom groups were not necessarily mutually exclusive. We used standard definitions for sensitivity, specificity, positive predictive value, and negative predictive value to identify the test characteristics for each of the types of incontinence symptoms. A urodynamic diagnosis of pure hypermobility genuine stress incontinence was used as the reference standard. We then constructed logistic regression models incorporating the AHCPR guidelines for pure hypermobility genuine stress incontinence and other relevant clinical variables to evaluate the predictive ability of the guidelines in a subset of 447 patients for whom data on all variables were available. The specific criteria we used were as follows: Symptom was stress loss only. Leakage from the urethra was observed with stress on examination (positive stress test result). There were <14 nocturic episodes per week (corresponding to an average of <2 episodes per night). Diurnal frequency was > 2 hours (corresponding to the AHCPR criterion of <8 episodes per day). Patient had no previous prolapse or incontinence surgery. Urethral hypermobility (>20 with Valsalva maneuver 17 ) was demonstrated. Postvoid residual volume was <100 ml. Other criteria considered were race and age. We plotted the receiver operating characteristic curves with sensitivity (the true-positive rate) on the y axis versus 1 Specificity (the false-positive rate) on the x axis. A model with good discrimination would have a high true-positive rate (here a correct diagnosis of genuine stress incontinence) with the false-positive rate remaining low. Each curve was evaluated with a unique measure of discrimination of the model, the C statistic, which corresponded to the area under the curve. The C statistic may range from 0.5 to 1.0, with a perfectly predictive model having a C statistic of 1.0. We calculated C statistics for each logistic regression model. The SAS (version 6.12; SAS Institute, Inc, Cary, NC) statistical software package was used for all statistical analyses. Results Table I displays the demographic distribution of our population. A total of 447 of the 950 patients were included in the regression analysis. These 447 patients were not significantly different from the whole group in terms of age, parity, weight, race, surgical history, and severity of incontinence. Table II indicates the distributions of urinary incontinence symptoms. A χ 2 analysis revealed that the distribution of symptoms among the patients included in the regression models did differ significantly from that among those excluded. Notably, however, a majority in both groups reported some form of stress urinary incontinence, half had mixed symptoms, and a third had stress urinary incontinence only. Table III displays the final urodynamic diagnoses. The distribution of diagnoses was comparable to those in other large series, with half of subjects having pure genuine stress incontinence. In keeping with symptomatic differences we found between the included group (n = 447) and the excluded group (n = 503), significant differences between groups also existed in the distribution of diagnoses. Patients with a diagnosis of detrusor instability represented the most striking difference, with a prevalence in the regression group half that among those excluded. It is interesting that a greater percentage of women in the regression group had intrinsic sphincteric deficiency.

4 Volume 184, Number 2 Weidner et al 23 Table II. Subjects grouped according to presenting symptoms Patients in regression analysis (n = 447) Patients excluded (n = 503) No. % No. % Any stress urinary incontinence Primarily stress urinary incontinence Stress urinary incontinence only Stress urinary incontinence and urge urinary incontinence Urge urinary incontinence only (no stress urinary incontinence) Constant and stress urinary incontinence Constant urinary incontinence Of the total 950 patients, 447 were included in the regression analysis and 503 were excluded because of missing data. The χ 2 analysis proved the distributions of the 2 groups to be different (P <.0001). Table III. Final urodynamic diagnoses Patients in regression analysis (n = 447) Patients excluded (n = 503) No. % No. % Genuine stress incontinence Detrusor instability Genuine stress incontinence plus detrusor instability Intrinsic sphincteric deficiency Normal study result Other diagnoses The 447 patients in the regression analysis and the 503 who were excluded are compared. The distributions of diagnoses were different (P <.0001, χ 2 test), with fewer patients with detrusor instability and more with intrinsic sphincteric deficiency in the regression group. Table IV. Accuracy (test characteristics) of presenting symptoms for a urodynamic diagnosis of pure hypermobility genuine stress incontinence (n = 950) Positive predictive Negative predictive Symptom Sensitivity (%) Specificity (%) value (%) value (%) Any stress urinary incontinence Primarily stress urinary incontinence Stress urinary incontinence only Stress urinary incontinence and urge urinary incontinence Constant urinary incontinence and stress urinary incontinence Constant urinary incontinence Table IV shows the sensitivity, specificity, and positive and negative predictive values for a urodynamic diagnosis of pure hypermobility genuine stress incontinence for each of the stress urinary incontinence symptom groups in the total population. Although a report of any stress urinary incontinence was sensitive, its specificity and positive predictive value were quite poor. The symptom classification of primarily stress urinary incontinence was somewhat more specific. The symptom of stress urinary incontinence only was the least sensitive but the most specific, and it also has a higher positive predictive value than did any other large symptom group. Mixed incontinence (stress urinary incontinence and urge urinary incontinence) was a poor predictor of pure genuine stress incontinence according to all measures. The symptom groups of constant and stress loss and constant loss contained too few patients for valid analysis. The AHCPR criteria appeared somewhat better than patient symptoms alone for the prediction of genuine stress incontinence. Table V shows the test characteristics and the prevalence of each individual criterion among the 447 patients for whom all clinical data were available. The relatively high prevalence of positive stress loss and urethral hypermobility (75%) and the associated good sensitivity and fair specificity resulted in the highest positive and negative predictive values of any AHCPR criteria. The other criteria were not so predictive. White race and young age have been associated with a higher likelihood of pure genuine stress incontinence. The specificity of white race as a criterion for the diagnosis of genuine

5 24 Weidner et al January 2001 Table V. Accuracy (test characteristics) of AHCPR criteria and other common clinical parameters (race and age) for urodynamic diagnosis of pure hypermobility genuine stress incontinence and frequency in study population (n = 447) Patients with parameter (n = 447) Positive predictive Negative predictive Parameter Sensitivity (%) Specificity (%) value (%) value (%) No. % AHCPR criteria Positive stress test result * 74.9 Hypermobility No history of surgery Normal postvoid residual volume Normal voiding White race Age <60 y *Only 257 of the 335 women with positive stress test results also had urethral hypermobility. The χ 2 analysis revealed no significant relationship between these 2 parameters. Straining urethral angle >20. Postvoid residual <100 ml. Daytime frequency 2 h and average of 14 episodes nocturia per week. Table VI. Comparison of regression models with AHCPR criteria and other clinically relevant variables used in models to predict diagnosis of pure hypermobility genuine stress incontinence, with C statistics of each model (n = 447) Patients meeting all model criteria AHCPR criteria (n = 447) No previous Normal Stress urinary Positive urologic or postvoid incontinence as stress incontinence residual Normal White Age C Model only symptom test result Hypermobility surgery volume voiding race <60 y statistic No. % A Used B Used Used C Used Used Used Used Used Used D Used Used Used Used Used Used Used E Used Used Used Used Used Used Used F Used Used Used Used Used Used Used Used G Used Used Used Used Used H Used Used Used Used Used stress incontinence was poor, which indicates a high-false positive rate and low positive predictive value. This was probably related to the high prevalence of white women in our population. The age distribution of the 447 women followed a bimodal distribution around the age of 60 years. We therefore used an age of 60 or <60 years as a dichotomous variable and calculated its accuracy for predicting a diagnosis of genuine stress incontinence. The positive and negative predictive values of an age of <60 years were similar to those of the positive stress test result. We then used the AHCPR criteria, white race, and age of <60 years to construct various logistic regression models and evaluate their abilities to predict pure hypermobility genuine stress incontinence. The characteristics of each model are shown in Table VI. Model A used the symptom of stress urinary incontinence only as the sole criterion. One third of the women reported this symptom. The C statistic for this model was only 0.574, which indicates that women who had this symptom frequently had a diagnosis other than pure hypermobility genuine stress incontinence. Model C, in comparison, used all the AHCPR criteria and had a higher C statistic of However, it applied to only 7.8% of women. The remainder of Table VI describes regression models that included different combinations of the AHCPR criteria, race, and age. Models that included the AHCPR criteria plus either white race or age <60 years, or both (D, E, and F), were slightly better at predicting pure hypermobility genuine stress incontinence. However, the additional variables limited the applicability of each model to an even smaller segment of the study population (5.4%-

6 Volume 184, Number 2 Weidner et al 25 Table VII. Evaluation of various models with respect to prediction of pure genuine stress incontinence for patients with urodynamic diagnoses other than pure hypermobility genuine stress incontinence (n = 447) Actual diagnoses when pure genuine stress incontinence was predicted by model Diagnosis Diagnosis relative Women meeting Pure genuine contraindication contraindication criteria of model stress incontinence for surgery* for surgery (n = 447) Model No. % No. % No. % No. % C (AHCPR criteria) G H Videla and Wall Models were as described in Table VI, except for the Videla and Wall 1 model, which used the symptom of primarily stress urinary incontinence, leakage with stress on examination, postvoid residual volume of 50 ml, and functional bladder capacity of 400 ml to predict a diagnosis of pure hypermobility genuine stress incontinence. *Diagnosis according to urodynamic evaluation was detrusor instability or a normal study result, with no genuine stress incontinence demonstrated. Diagnosis according to urodynamic evaluation was genuine stress incontinence plus detrusor instability, intrinsic sphincteric deficiency, or intrinsic sphincteric deficiency plus detrusor instability. Percentage of patients meeting model criteria for predicted diagnosis of pure genuine stress incontinence. 7.0%). Overall the AHCPR variables of normal postvoid residual volume and normal voiding were the least significant, with odds ratios that were not substantially different from 1.0 and confidence limits that contained 1.0. Models that excluded these 2 variables (G and H) included slightly more women (13% and 10.1%, respectively) without any effect on accuracy. Because one purpose of the AHCPR criteria is to allow the clinician to bypass multichannel urodynamic studies in the workup of a surgical patient, we evaluated the ability of these models to exclude patients with urodynamic diagnoses that were relative or absolute contraindications to surgical management. We selected the 3 best models (C, G, and H) for this analysis (Table VII) and compared them with a model proposed by Videla and Wall. 1 We considered both a urodynamic diagnosis of detrusor instability and a normal urodynamic study result to be absolute contraindications to surgical treatment. Diagnoses of genuine stress incontinence plus detrusor instability, intrinsic sphincteric deficiency, or intrinsic sphincteric deficiency plus detrusor instability were regarded as relative contraindications to the usual continence procedures performed by gynecologists (Burch and Marshall- Marchetti-Krantz urethropexies). 20 Two of the 35 women predicted by the AHCPR criteria (model C) to have pure hypermobility genuine stress incontinence ultimately had pure detrusor instability diagnosed at urodynamic examination. In contrast, models G and H excluded all patients who had either detrusor instability or normal urodynamic study results and applied to more women, although still a minority of patients. All 3 models erroneously predicted pure hypermobility genuine stress incontinence in a small number of women with relative contraindications to surgery (model C, 8.6%; model G, 13.7%; and model H, 11.1%). A model constructed with the criteria proposed by Videla and Wall 1 predicted 79 women to have pure hypermobility genuine stress incontinence, including 3 women with absolute contraindications to surgery and 30 women with relative contraindications. The Videla and Wall 1 model s C statistic for prediction of the diagnosis of pure genuine stress incontinence was Only a minority of women met the criteria for any of the models in Table VII, ranging from 7.8% for the AHCPR model to 25.1% for the Videla and Wall 1 model. In an effort to simulate a primary gynecologic practice population, we reanalyzed models G and H with only women with no previous urogynecologic surgery (284/447). The C statistics of both models improved slightly, to and 0.858, respectively, and both models excluded all women with detrusor instability or normal urodynamic study results. Although we anticipated that this would preferentially select women with less complicated incontinence who were more likely to have a diagnosis of pure genuine stress incontinence, the fractions of women meeting all the criteria of the 2 models were still only 15.8% for model G and 16.5% for model H. Comment The first objective of this study was to evaluate the accuracy of various symptoms of stress urinary incontinence in the diagnosis of the condition of pure hypermobility genuine stress incontinence. Multiple previous investigators have noted the insensitivity of incontinence symptoms as the sole predictor of a urodynamic diagnosis of genuine stress incontinence, 3, 5, and our results validate such findings. We found that even pure stress loss symptoms had a positive predictive value for genuine stress incontinence of only 73.7%, even in the context of a 53.4% prevalence of the diagnosis. This observation was

7 26 Weidner et al January 2001 validated by the low C statistic for the model that used only pure stress loss. Furthermore, only a minority of patients with stress loss had pure symptoms. The discriminatory abilities of various combinations of mixed symptoms were even less reliable. Therefore even in the best of circumstances (pure symptoms and a prevalent condition) symptoms alone provided insufficient assurance to allow a clinician to undertake surgical intervention to treat genuine stress incontinence. Because just such an assurance is a goal of the AHCPR criteria, we performed a similar analysis of these criteria. Taken individually none of the criteria had positive or negative predictive values adequate for selection of surgical treatment. The most helpful was the clinical observation of loss of urine with a stress test, which had a positive predictive value of 68.2%; this criterion s higher negative predictive value of 88.6% indicates that a negative stress test result was more helpful to rule out the diagnosis of genuine stress incontinence than a positive one was to support it. Although each criterion was met by a majority of women, only 35 of 447 women (7.8%) met all criteria. Although the AHCPR model was a reasonably good predictor of genuine stress incontinence (C statistic of 0.807) in our population, <1 in 12 women were eligible for surgical treatment on the basis of the model without some form of urodynamic testing. Although the model that incorporated all AHCPR criteria plus age and race was the most predictive (C statistic of 0.833), it was also the most restrictive, applying to only 5.4% of subjects. By eliminating the statistically insignificant variables of normal voiding and normal postvoid residual volume and adding the variables of white race and age <60 years we found models that provided the best combination of predictive ability and applicability. These models applied to twice as many subjects without a significant loss in discrimination. The appropriate initial management of mixed urinary incontinence remains controversial, 20, 24 and it is unclear whether initial management with surgery designed to treat the stress component of the incontinence is likely to worsen or improve the urge component. Intrinsic sphincteric deficiency, although a type of stress incontinence, is a diagnosis that lacks a consensus definition. 17 Stabilization of the bladder neck through retropubic procedures may fail to correct incontinence caused by intrinsic sphincteric deficiency. With these ideas in mind we considered genuine stress incontinence plus detrusor instability, intrinsic sphincteric deficiency, and intrinsic sphincteric deficiency plus detrusor instability as relative contraindications for surgery. We considered pure detrusor instability and normal urodynamic study results to represent absolute contraindications to surgery, because women with these diagnoses would not logically be expected to have any benefit from surgery. Our results suggest that models G and H may have been the most conservative because of their ability to exclude the most women who would have had diagnoses contraindicating surgery. Both models G and H did a better job of excluding women with absolute contraindications to surgery than did the AHCPR criteria, with only a small number of women with relative contraindications, while applying to a larger portion of the population. These observations were true whether model G or H was applied to our population or to the subset of our population that had no history of urogynecologic surgery. The model proposed by Videla and Wall 1 was less restrictive than either model G or H and applied to fully a quarter of our regression population while still excluding all but 3 women who ultimately were found to have pure detrusor instability or normal study results. However, this model was not nearly as good at excluding women who had mixed incontinence or intrinsic sphincteric deficiency at urodynamic evaluation. It predicted a diagnosis of pure hypermobility genuine stress incontinence for 30 such women, a quarter of all the women in the model. In the absence of good evidence on the outcomes of surgery for genuine stress incontinence among women with mixed incontinence, the choice of the appropriate model must be based on clinical judgment. Clinicians who believe that women with mixed incontinence frequently have improvement after surgery to treat the stress component may find the Videla and Wall 1 model the most useful. There were several limitations to our study. Our referral population may not have been entirely representative of women seeking treatment at a nonreferral practice. We were frustrated by missing data, which prevented us from including all patients in the regression analysis and forced us to analyze a group of women who had a distribution of diagnoses slightly different from that in our larger group. We theorize that women with certain types of incontinence, such as detrusor instability, might have been preferentially excluded from the regression analysis because the cause of the incontinence was readily apparent during urodynamic testing, which thus resulted in less rigorous collection of all diagnostic parameters. We recognize that multichannel urodynamic testing is an imperfect diagnostic method that is both expensive and not widely available. However, it is clear that reliance only on clinical models to determine which patients should undergo surgery would result in extremely inappropriate treatment for some patients. No model applied to more than a quarter of the population, and most applied to far fewer women. Our analysis supports routine urodynamic evaluation for most women with incontinence symptoms before embarkation on surgical treatment. REFERENCES 1. Videla FL, Wall LL. Stress incontinence diagnosed without multichannel urodynamic studies. Obstet Gynecol 1998;91: Swift SE. The reliability of performing a screening cystometro-

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