https://orcid.org/0000-0002-8127-7153
Abstract
Aims: Intermittent catheterization (IC) is the gold standard for bladder management in patients with chronic urinary retention. Despite its medical benefits, IC users experience a negative impact on their quality of life (QoL). For health economics based decision making, this impact is normally measured using generic QoL measures (such as EQ-5D) that estimate a single utility score which can be used to calculate quality-adjusted life years (QALYs). But these generic measures may not be sensitive to all relevant aspects of QoL affected by intermittent catheters. This study used alternative methods to estimate the health state utilities associated with different scenarios: using a multiple-use catheter, one-time-use catheter, pre-lubricated one-time-use catheter and pre-lubricated one-time-use catheter with one less urinary tract infection (UTI) per year.
Methods: Health state utilities were elicited through an internet-based time trade-off (TTO) survey in adult volunteers representing the general population in Canada and the UK. Health states were developed to represent the catheters based on the following four attributes: steps and time needed for IC process, pain and the frequency of UTIs.
Results: The survey was completed by 956 respondents. One-time-use catheters, pre-lubricated one-time-use catheters and ready-to-use catheters were preferred to multiple-use catheters. The utility gains were associated with the following features: one time use (Canada: +0.013, UK: +0.021), ready to use (all: +0.017) and one less UTI/year (all: +0.011).
Limitations: Internet-based survey responders may have valued health states differently from the rest of the population: this might be a source of bias.
Conclusion: Steps and time needed for the IC process, pain related to IC and the frequency of UTIs have a significant impact on IC related utilities. These values could be incorporated into a cost utility analysis.
Introduction
Ever since the introduction of the clean technique by Lapides in 1972, intermittent catheterization (IC) has been recognized as the gold standard for bladder emptying in people suffering from chronic urinary retentionCitation1. Studies have subsequently demonstrated several medical as well as social benefits of IC, including fewer urinary tract infections (UTIs), increased independence and ability to enjoy intimacy and sexual activitiesCitation2–4.
However, IC also brings challenges, such as requirement to perform multiple daily catheterizations, finding access to clean water, the preparation of the catheter and, in case of multiple-use catheters, efforts involved in storage, cleaning and drying of catheters after each use. There are also concerns related to discomfort and pain due to the repeated insertion and removal of catheters for some patientsCitation5. For these and other medical related reasons (e.g. urethral complications), a substantial proportion of IC users change to other bladder management solutions (such as indwelling catheters), which have poorer safety profilesCitation4,Citation6,Citation7.
Innovations in catheter design and technology have appropriately focused on making the IC process easier as well as less painful, and have resulted in the introduction of one-time use and hydrophilic coated catheters. To document the impact of urinary disorders and catheter properties on quality of life, condition specific measures such as ISC-Q (Intermittent Self-Catheterization Questionnaire) and Qualiveen have been developed and validatedCitation8,Citation9. However, the data from these tools is not suitable for health economic evaluations because the scores from the measures are not preference weighted. Preference weighting is a requirement in economic evaluation because it indicates the value of quality of life statesCitation10. Since innovative catheter technologies are more expensive than basic catheters, health economic evaluations have been requested as evidence to inform decision makers responsible for access to intermittent cathetersCitation11. Further, it has been specifically pointed out that cost effectiveness studies on IC should include patient acceptability/satisfaction with the procedure as well as the productCitation12.
The usage of a common metric such as quality-adjusted life year (QALY) makes comparison of benefits across therapeutic areas possible; these results can be used for cost utility analyses. QALYs are useful because they combine length and quality of life and are calculated from utility values, which quantify health-related quality of life (HRQoL) on an interval between 0, signifying dead, and 1, which is full healthCitation13. To maintain consistency and comparability, health technology assessment organizations normally recommend that utility values are obtained through generic questionnaires such as EQ-5DCitation14. However, in some circumstances generic measures can lack sensitivity as well as content validity and researchers then have to rely on disease specific measures or alternative methods. It has also been suggested that generic measures are not well suited for assessing QoL aspects related to the process of using medical devicesCitation10,Citation14 and that EQ-5D is therefore unlikely to be able to capture the effects of specific improvements in intermittent catheter designCitation15.
Among the various alternative methods available for eliciting utility values, the valuation of health states (or vignettes) using the time trade-off (TTO) approach is widely usedCitation16. This approach is well suited for isolating the utility impact of specific treatment processesCitation17. This approach is also mentioned in the guidelines on health economic evaluations from several authorities, when generic tools are not appropriate or sufficientCitation18,Citation19.
The purpose of the current TTO study was to investigate the impact on health state utilities associated with four different aspects of urinary catheters: steps required for IC, time needed for the IC process, pain related to IC and frequency of UTIs.
Methods
Vignette based time trade-off method
The TTO method is a tool used for eliciting utility values ranging from 0 to 1 by asking respondents to “trade” a part of their remaining life against gains in quality of life. A vignette or health state is a description of how it is to live with the specific health condition and focusing on some of the characteristics related to the study area. One scenario offers the respondent a defined health state for a lifetime, t, while the other scenario offers a better health state for a shorter lifetime, x. The shorter lifetime, x, is varied and the questions repeated until the two scenarios are equally attractive to the respondent; this point is known as the “indifference point”, x*. At the indifference point, the preference score for that specific health state is given as: x*/t, which corresponds to the estimate of the utilityCitation20,Citation21.
Health states
In our survey, the respondents were first presented with a health state scenario designed as a “warm-up” exercise to familiarize them with the subject and the TTO methodology. contains the warm-up text describing what it means to be using a catheter.
Figure 1. Description of what it means to use an intermittent catheter.
Four different health states were developed, based on three types of technologies within IC: (a) a catheter that is used multiple times and cleaned between storages (also defined as re-use); (b) a one-time use catheter which needs manual lubrication (also defined as uncoated catheter); and (c) a one-time use catheter that is ready to use from its packaging (also defined as hydrophilic coated catheter). For each health state four attributes were identified to describe the differences between the technologies: (1) the steps and (2) time needed for catheterization; (3) pain level; and (4) frequency of UTIs.
User experiences with IC vary considerably between persons and to ensure representativeness the wording/attributes/levels were based on previous IC researchCitation5,Citation22–24 with participation of more IC users than a limited number of explorative interviews would have allowed. The health states were reviewed by five medical doctors amongst the authors, who all have extensive clinical experience with the use of IC, to ensure that the wording was representative of the investigated topics. The steps needed for catheterization were described in three levels based on Wilks et al.Citation24, the two pain levels were based on Stensballe et al.Citation5, the two UTI levels were based on Krassioukov et al.Citation23 and reduction from Cardenas et al.Citation22. No published references were found for the average time spent on the total catheterization process for the three respective catheter technologies. One study reported an average intermittent catheterization time of 16 minutes in a pediatric spinal cord injured population, but the result was not found to be generalizable to the larger IC population and therefore was not usedCitation25. In lack of relevant published references, the levels were based on the experiences of the authors and not worded in exact minutes (e.g. “up to 6 minutes”). The time necessary for catheterization comprises: (a) time for preparation; (b) time for insertion of the catheter; (c) time during which the catheter remains in the bladder, depending upon the bladder filling volume as well as the lumen of the catheter; and (d) post-catheterization tasks, such as disposal or packaging of the catheter materials. Thus, the total time is expected to vary from person to person. The catheter attributes and levels in each health state were described using simple lay terminology before the actual TTO questions. The health states are summarized in .
Table 1. Health states and levels.
The survey
The study was conducted as an online survey in a representative Canadian general population sample in March 2017 and in a representative UK general population sample in April 2017. The general population sample was used in line with best practice in economic evaluationCitation13. Canada and the UK were selected because both countries use cost utility analysis with the QALY as preferred outcome measure in their evaluation of medical interventions. All respondents were aged 18 years old or above and were recruited from existing email panels provided by an online analysis company. Representativeness was assessed based on the respondents’ age, gender, household size and income. The online survey method allowed for additional invitations targeted to the parts of the overall population that were missing in order to reach a representative sample. The respondents had previously agreed to participate in an internet-based survey and remained anonymous throughout the study. Additionally, the survey was carried out within the codes of conduct of the Market Research Society and following the applicable ESOMAR guidelines. The respondents received a link to the online survey and each link could only be answered once. After completing the survey, the respondents were offered a compensation of £1/$1 for their time. Ethical review board approval was not required for this type of study in the UK or Canada, since it was not a clinical trial, did not include patients, and did not collect human or biological samples or identifiable personal information.
The questionnaire was composed of four different health states with associated TTO questions. Utility values were obtained from the survey by asking respondents to “trade off” a portion of their remaining lifespan for an improved health state. To make the trade-offs as realistic as possible, the time horizons used were based on each respondent’s projected life expectancy accounting for country, gender and age of the respondents, obtained from the World Health Organization life tablesCitation26. An example question for health state 2 (HS 2) describing one-time use catheters is shown in with xx representing the time horizons, which depended on the specific respondent’s life expectancy.
Figure 2. Example of TTO survey question.
The functionality of the questionnaire was validated in a pilot study consisting of 20 respondents. The TTO exercise involved a complicated routing through the online questionnaire. This is due to the dynamics of the TTO questions, where the next trade-off depends on previous answers and the random ordering of the health states. By analyzing the data from the pilot study, it was validated that the respondents had received the right TTO questions in each of the health states and that the health states were shown in the right order. To test respondents’ understanding of the TTO concept, a test question was included offering a choice of: (1) full health and a longer remaining lifetime; or (2) less than full health and a reduced lifetime. Respondents choosing the second option were excluded from the analysis, as this could reflect inability to understand the method. To identify the point where both options are equally acceptable, respondents were asked the question four to six times, varying only the number of years living in full health. This procedure followed standard bisection methodology, using a starting point of utility = 0.6 to reduce the utility value down to an interval of 0.025.
Responses were excluded if they did not understand the question or did not want to participate in the TTO method. The order of the health states was randomized to avoid respondent fatigue bias and to ensure that respondents valued the health states individually and not relative to each other.
The online questionnaire was programmed in a commercial survey software package, SurveyXact. To improve the answer quality and prevent unconsidered responses, a 10 second delay was introduced to pages containing essential text.
Statistical analysis
All statistical analyses were performed using SAS version 9.4 statistical software. A utility value was assigned to each health state based on individual responses, derived from the midpoint of the indifference interval as described above. Based on all respondents’ individual utility values, the average utility value was calculated for each health state. To get the additional value of one health state or attribute compared to another, the average utility values of the two health states were subtracted. As an example, HS 4 is only different from HS 3 in terms of yearly UTIs (3 vs. 4 UTIs per year) and the difference between the two health states therefore shows the utility gain from 1 less UTI per year. Similarly, the difference between HS 4 and HS 1 indicates the utility value associated with the combined attributes of less steps/time needed for catheterization, pain and UTIs, which would resemble the difference between a ready-to-use hydrophilic coated catheter and a multiple-use catheter.
Bootstrapping was used to simulate standard errors and confidence intervals (CIs) for the mean TTO values, as the response distribution was unknown but suspected to be non-normal and non-parametric. This method estimates the parameter’s distribution by repeatedly resampling the original data set with replacementsCitation13. For the present study, 10,000 iterations were performed.
The 5% most extreme values were excluded from the base analysis (2.5% in each end) to ensure better confidence in the results. A sensitivity analysis was carried out to investigate the consequences of outliers on the utility values. Participant inclusion of 100%, 99% and 90% were investigated in the sensitivity analysis.
Results
A total of 1028 respondents (518 respondents from Canada, 510 from the UK) completed the questionnaire. A total of 33/518 (6.37%) of the Canadian respondents and 39/510 (7.64%) of the UK respondents failed the test question by preferring a health state with less than full health and a reduced lifetime. This failure rate is within the range of similar studiesCitation27,Citation28. After excluding these respondents, the remaining analysis was done for 956 respondents (485 from Canada, 471 from UK). Online user panels are different from conventional postal surveys, so data is not recorded on non-responders, but only on the ones who click the link and participate. For this reason, a survey response rate cannot be reported. The demographic and socioeconomic characteristics of the respondents are shown in .
Table 2. Demographic and socioeconomic characteristics of the respondents used for analysis.
Both in Canada and in the UK, incrementally higher utility gain was associated with one-time use catheters (less steps/time needed), ready-to-use catheters (less steps/time needed and less pain) and with a reduction of 1 UTI per year.
The incremental utility values for each health state elicited by the TTO method are reported in , which contains the isolated utility values related to the specific attributes as well as the utility values of the combined attributes representing different types of catheters available for patients.
Table 3. Incremental utility results with 95% confidence intervals (CIs) for UK and Canada.
The table shows that the total health state utility gain associated with a catheter containing all the desirable attributes was slightly higher for the UK (+0.049) than Canada (+0.041), based on a higher preference for the one-time use feature in the UK. This difference resembles the technology of ready-to-use hydrophilic coated catheters compared to re-usable catheters. The technology resembling ready-to-use hydrophilic coated catheters yielded a utility gain of +0.027 in Canada and +0.028 in the UK compared to uncoated single-use catheters. All results were statistically significant.
The sensitivity analysis showed that increasing the cut off percentage of outliers (from 1% to 10%) corresponded with lower gains in utility associated with IC. This was true for “single use” and “ready to use” attributes. However, this increase in cut-off did not impact the “frequency of UTI” attribute. This suggests that some outliers are having a disproportionate effect on the average gain in utility. The sensitivity analysis is depicted in .
Figure 3. Utility sensitivity results for UK and Canada with participant inclusion at 100%, 99%, 95% (primary analysis) and 90%. Outlier utility values were cut from both ends of the distribution. Abbreviation. UTI, urinary tract infection.
Discussion
Using the TTO method, the current study showed that fewer steps and less time needed for catheterizing, reduced pain, and fewer UTIs were associated with increased utility values for IC. When all of the identified catheter attributes are aggregated into one catheter scenario, resembling a ready-to-use hydrophilic coated catheter, the incremental utility value compared to a re-usable catheter would be +0.041 in Canada and +0.049 in the UK.
The study shows that the TTO vignette method can be a useful alternative when the standard generic methods for arriving at QALYs are not sensitive to relevant aspects of QoL. The elicited utility values provide a numeric expression of the benefits related to catheter technologies, and may be used as input parameters in future cost utility analysis (depending on the guideline for health economic evaluation in the specific geography).
There is an increasing recognition that the generic methods such as EQ-5D are not always sufficient in relation to some types of medical devices, including devices for ICCitation10,Citation14,Citation15. The rationale behind this argument is that some of the user benefits offered by medical devices may not be adequately captured by the dimensions of health included in the standard generic tools. This limitation of the generic methods might be particularly pronounced in relation to disposable medical devices such as intermittent catheters, which are normally aimed at long term or chronic conditions where process aspects related to daily usage are likely to impact QoL. In chronic conditions, the issues related to the treatment process, such as convenience, time spent and discreetness, are likely to play a significant role over a prolonged period. Further, the generic measures have also been criticized for not being able to measure small but, in the long term, important changes in QoLCitation14.
The TTO methodology has previously been used in utility assessments related to medical devices, albeit in different treatment areasCitation17,Citation27,Citation28. A survey based TTO study found that a once daily insulin injection yielded an incremental utility of 0.039 compared to twice daily injectionsCitation29. A recent interview-based TTO study found a significant utility difference of 0.03 between sensor-based glucose monitoring and conventional glucose monitoringCitation17. Previous TTO studies thus found process related utilities within the same range of our findings for intermittent catheters and the current study confirms that the TTO method can be used for direct elicitation of utility values, including those for medical devices.
To our knowledge, this is the first study to elicit utility values specifically for different features and benefits of IC and thus it is not possible to assess the clinical meaningfulness of the results by comparing with previous studies. Bermingham and Ashe in 2012 concluded in a literature review that very few studies have measured quality of life in patients with UTI using generic preference-based measures of healthCitation30. In a subsequent cost–effectiveness analysis, a mapping algorithm from SF-12 to EQ-5D was used by Bermingham et al. to estimate a utility loss of 0.049 per incident of UTICitation31. This value is substantially higher than the value of 0.011 found in our study. A possible explanation might be that Bermingham et al. focused on the UTI utility value in a short treatment period (normally 1–2 weeks) and did not include the worrying and anxiety for additional UTIs that are reported elsewhere in the literatureCitation32.
The results of the current study should be interpreted with the methodological strengths and limitations in mind. One of the advantages of the web based approach is that it can provide relatively large sample sizes compared to the interview based approach, for more robust results. The online recruitment system made it possible to recruit a respondent group that mirrored the general population in terms of age, sex and income. In the base analysis, all the utility values were statistically significant at a 95% CI, and the results were comparable for Canada and the UK, supporting the validity and reproducibility of the results. However, the online survey method potentially creates a risk of bias if internet users tend to value health states differently from internet non-users. Another possible weakness of the internet-based survey is that the descriptions of the health states might not have properly reflected the disadvantages and benefits of the different attributes. To limit this type of bias the health states were based on published references where possible and IC features were described objectively. However, no relevant references were located on time spent for catheterization and the levels were instead based on clinical experience among the authors and worded flexibly. The results have to be interpreted with these limitations in mind.
Utility values can either be elicited among the general population without personal experience about the condition in question, or among patients affected by the condition themselvesCitation33. In this study, utility values were elicited from the general public because this is recommended by most Health Technology Assessment (HTA) authoritiesCitation34. It would be relevant to carry out a similar study among actual catheter users to investigate both similarities and differences. Given the relatively high response consistency between the results from the UK and Canada, it would also be appropriate to investigate the impact on the results if the survey is carried out in countries with different health care financing or in countries with a lower level of health care innovation.
A number of methods can be used for eliciting utility values when the recommended generic tools are insufficientCitation33. Health utility values can be elicited using either direct or indirect methods. Direct measures of utility map preferences directly onto the utility scale using either standard gamble or TTO, while indirect measures rely on quality of life questionnaires (e.g. EQ-5D or SF-6D) which are converted to utility values via “weights” obtained from the general publicCitation35. Direct methods have been reported to create higher utility values than indirect methods but, since there is no accepted theoretical basis for choosing one over the other, practical implications have been suggested as a guide for choosing between themCitation35. In our case, the recommended indirect methods were not sufficient for the reasons mentioned above and direct elicitation was found to be an appropriate alternative. Within direct health state valuation, the standard gamble trade off approach has been found to result in generally higher utility values than the TTO methodCitation36. The TTO method is considered as an accepted compromise between simplicity and strict theory and is also the most widespread approachCitation37,Citation38. However, it would be relevant in future studies to compare the current results with utility values related to IC elicited using other methods, such as developing preference weights for an IC outcome measure, or by developing “bolt-on” items to EQ-5D. The chosen elicitation method can have a significant impact on the utility values and it is important to take this into consideration, e.g. in the sensitivity analysis, when using the current results in future cost utility analysis.
The accuracy of the health state descriptions is crucial for the validity of TTO-generated utility valuesCitation17. In the current study pain related to catheterization was especially difficult to describe and quantify, since it is inherently subjective. To ensure that the wording and levels represent the IC user’s actual experience on different types of catheters, the pain questions were based on the wordings in the scale used in a study by Stensballe et al., which included 40 participants in a blinded studyCitation5. It would be relevant for future studies to test how different wordings (e.g. “similar to a pin prick/bee sting”) with reference points easily understood by lay persons would influence the results.
Conclusion
The results of this study suggest that steps and time needed for the total IC process, pain related to IC and the frequency of UTIs have a significant impact on health state utilities. Catheter technologies that reduce the steps involved in IC, reduce pain levels and reduce the occurrence of UTIs are likely to improve QoL and may thus also have a potentially positive impact on long term adherence to IC. The utility values generated in this study may be used as expression of relative health benefits in cost utility analysis of different management options for urinary retention.
Transparency
Declaration of funding
Coloplast A/S provided research funding for Incentive Partners Aps for conducting the survey. Editorial services from Marksman Healthcare Communications and a critical scientific review by Andrew Lloyd were additionally supported by funding from Coloplast A/S.
Author contributions: Analysis conception and design, data analysis, manuscript draft preparation: M.A.A., A.K., N.T., H.M., M.B. and Y.I. Data collection, data and analysis tool contribution: M.B. Final draft approval: all authors.
Declaration of financial/other relationships
A.K., M.A.A., N.T. and Y.I. have disclosed that they occasionally provide expert knowledge to advisory boards and educational activities at Coloplast A/S. M.B. has disclosed that she is employed at Incentive Partners Aps. H.M. has disclosed that he has no significant relationships with or financial interests in any commercial companies related to this study or article.
Peer reviewers on this manuscript have received an honorarium from JME for their review work, but have no relevant financial or other relationships to disclose.
Acknowledgements
We gratefully acknowledge the support of Andrew Lloyd, Bladon Associates Ltd, for a critical review of the manuscript and Marksman Healthcare Communications, for editorial services. Jeppe Sørensen and Mia Buus Andersen, Coloplast A/S, contributed to the study design and conducted a scientific review of the manuscript.
Previous presentation: The results have not previously been presented. An abstract based on the initial results from the study (without outlier analysis) was accepted for poster presentation at the ISPOR conference, Baltimore, USA, 19–23 May 2018.
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