Increased Driving Distance to Screening Colonoscopy Negatively Affects Bowel Preparation Quality: an Observational Study

Abstract

Background

To prepare for colonoscopy, patients must consume a bowel purgative and travel from their home to the site of their procedure. The timing of bowel purgative ingestion predicts bowel preparation quality. Currently, it is not known if driving distance impacts bowel preparation quality or adenoma detection.

Objective

This study investigates the effect of driving distance on bowel preparation and adenoma detection.

Design

This is a cross-sectional retrospective analysis of outpatient screening colonoscopy procedures that were completed at an academic medical center.

Participants

A total of 5089 patients who completed screening colonoscopy across 3 procedure units were analyzed.

Main Measures

Description of bowel preparation was dichotomized to either adequate or inadequate. Patient residential addresses were converted into geographic coordinates for geospatial analysis of driving distance to their colonoscopy site.

Key Results

Median driving distance was 13.1 miles. Eighty-nine percent of patients had an adequate bowel preparation. The rate of adenoma detection was 37%. On multivariable logistic regression adjusting for age, sex, race, insurance, endoscopist, and site, increasing driving distance (10-mile increments) was negatively associated with adequate bowel preparation (odds ratio = 0.91; 95% confidence interval 0.85 to 0.97), while adenoma detection was positively associated with adequate bowel preparation (odds ratio = 1.53; 95% confidence interval 1.24 to 1.88) but not with driving distance (odds ratio = 1.02; 95% confidence interval 0.98 to 1.06). Driving distances of 30 miles or less were associated with adequate bowel preparation (odds ratio = 1.37; 95% confidence interval 1.09 to 1.72).

Conclusions

Increasing driving distance to screening colonoscopy was negatively associated with adequate bowel preparation but not adenoma detection. Among an academic medical center population, the likelihood of adequate bowel preparation was highest in patients traveling 30 miles or less to their screening colonoscopy. Patient driving distance to colonoscopy is an important consideration in optimizing screening colonoscopy quality.

INTRODUCTION

Guideline-adherent colorectal cancer (CRC) screening is known to increase early detection and reduce mortality related to colorectal cancer. While there are a multitude of screening tests available, only colonoscopy every 10 years and annual fecal immunochemical test are considered first-tier.^1,2 Among these tests, colonoscopy is the most commonly used CRC screening test in the USA and only colonoscopy allows for simultaneous polyp detection and removal.^3,4 One challenge inherent in colonoscopy is the need for an adequate bowel preparation, as adenoma detection, diagnostic accuracy, safety, and the ability to follow recommended screening and surveillance guidelines depend on it.^3,5 Higher quality preparation is associated with increased detection of both small and large polyps.^6,7 Conversely, inadequate preparation leads to increased rates of missed lesions, interval cancers, and cost.^7–12 In this context, the American Society for Gastrointestinal Endoscopy (ASGE)/American College of Gastroenterology (ACG) Task Force on Quality in Endoscopy has provided recommendations for documentation of the quality of preparation, a target of adequate bowel preparation in at least 85% of outpatient examinations, and an adenoma detection rate of at least 25% for average-risk individuals undergoing screening colonoscopy.^3,13

Unfortunately, current studies suggest that the adequate bowel preparation target is not universally being met, as preparation is inadequate for almost a quarter of patients undergoing colonoscopy in some settings.^7,11 Identifying factors that may contribute to suboptimal bowel preparation is important in determining opportunities for improvement. Prior studies have identified a multitude of such factors. These include the following: low patient activation, failure to follow preparation instructions, lower socioeconomic status, decreased English proficiency, lack of social support, increased age, male gender, history of diabetes, cirrhosis, stroke, or dementia, procedural indication of constipation, use of tricyclic antidepressants, medical regimen complexity, inpatient status, failure to use split-dose preparations, and afternoon procedure time.^3–5 Moreover, recent studies also indicate that the timing between the last dose of purgative and the time of the colonoscopy correlates with the quality of the bowel preparation.^14–19

Increased distance to healthcare has been shown to have a negative impact on health outcomes in multiple different contexts including but not limited to diabetes management, breast and colorectal cancer survival, post-operative complication rates in various surgical settings, acute coronary syndrome, and stroke.^20–24 Outpatient screening colonoscopy quality may likewise be negatively impacted by distance, especially given that (1) patients must consume an oral purgative and travel from their home to an endoscopy site for their procedure and (2) healthcare-related infrastructure is often concentrated in urban and suburban areas.^16,25 However, no prior study to our knowledge has investigated whether distance to the site of endoscopy has an effect on bowel preparation quality, and consequently, adenoma detection. We hypothesized that increased distance to the site of endoscopy would negatively impact bowel preparation quality, as well as adenoma detection.

METHODS

Study Design

This study is a cross-sectional retrospective analysis of outpatient screening colonoscopy procedures performed at the University of Michigan over a 1-year period, beginning January 1, 2017, through December 31, 2017. The study received IRB approval (protocol number: HUM00144385).

Setting

Michigan Medicine (MM) is the academic medical center of the University of Michigan. MM includes multiple hospitals and outpatient health centers. During the study interval, outpatient gastrointestinal endoscopies were performed primarily at one of three medical procedures units: the University Hospital Medical Procedures Unit (UH MPU) in Ann Arbor, East Ann Arbor Health Center Medical Procedures Unit (EAA MPU) in Ann Arbor, and the Northville Health Center Medical Procedures Unit (NHC MPU) in Northville, Michigan. MM faculty may perform endoscopies primarily at a single site or rotate across sites. MM patients who are completing outpatient screening colonoscopies are given a choice to schedule their procedure at their preferred location.

Patients who are scheduled for colonoscopy receive standardized written instructions for bowel preparation. At MM, the standard practice for colonoscopy bowel preparation is a clear liquid diet the day before the procedure and 4 L of polyethylene glycol-electrolyte lavage solution, taken as a split-dose regimen, with 2 L taken on the day of the procedure. A description of the bowel preparation quality and confirmation of cecal intubation were documented using commercially available procedure documentation software, ProVation MD (ProVation®Medical Minneapolis, MN). Preparation quality was described using a 4-point scale of excellent, good, fair, or poor, as well as the total Boston Bowel Preparation Scale that can range from 0 to 9.^26–28 Procedure documentation software also included subjective preparation descriptors such as adequate, inadequate, and unsatisfactory. In accordance with prior studies evaluating bowel preparation quality, descriptions were dichotomized to either adequate (excellent, good, adequate, or BBPS ≥ 6), or inadequate (BBPS < 6, fair, poor, unsatisfactory, or inadequate).^7,11,29,30

Study Participants

Patients who completed an outpatient screening colonoscopy performed at MM during the study interval were eligible for study inclusion. Screening colonoscopies were identified using ICD-10 codes for the following: colorectal cancer screening, colonoscopy on individual not meeting criteria for high risk; colorectal cancer screening, colonoscopy on individual at high risk; and colonoscopy, with removal of tumors, polyps, or lesions by snare technique.

Exclusion criteria for the study included age less than 45 years or greater than 75 years; history of colon, rectal, or anal cancer; history of adenomatous polyps; inflammatory bowel disease; hereditary colon cancer syndrome; history of surgery on the colon or rectum; and incomplete colonoscopy due to complex anatomy (colon tortuosity). The inclusion and exclusion criteria were adopted to select a patient population who completed a screening colonoscopy with no personal history of colorectal cancer or adenomatous colon polyps. Finally, in accordance to the stated study objectives, individuals with a Post Office box as their documented residential address and colonoscopies with no documentation of bowel preparation description were excluded from the final analysis.

Geospatial and Statistical Analysis

The addresses of the three Medical Procedure Units and the residential addresses of patients who completed a colonoscopy during the study interval were converted into geographic coordinates based upon their point locations. To calculate the driving distance to the site of screening colonoscopy, we used an origin destination matrix describing the network based distance with the patients’ residential point locations as the origin and the procedure units’ point locations as the destination. Travel time and travel distance measurements were calculated for automobiles using public roads exclusively with observance of speed limits and traffic restrictions. Traffic conditions such as the day of the week and time of day were not considered in the analysis. The measurement for travel distance in miles was selected to represent driving distance and converted into a categorical variable with 10-mile increments.

Continuous variables were compared using the Kruskal-Wallis equality-of-populations rank test. Categorical variables were analyzed using the Pearson chi-square, Fisher’s exact test, or logistic regression where appropriate.

The study covariates included patient demographic characteristics: age (years), sex (male or female), race (White, Black, Asian, or refused/not recorded), health insurance (Private, Medicare, Medicaid, or TRICARE); driving distance to procedure site (miles); procedural site (East Ann Arbor, University Hospital, or Northville Health Center); endoscopist; and the study outcomes: bowel preparation (adequate or inadequate) and adenoma detection. In addition, the effect of driving distance to the procedure site on the colonoscopy process measures total procedure time (minutes) and colonoscopy withdrawal time (minutes) were also examined. All analyses were conducted using StataMP version 16 (StataCorp CP College Station, TX). A two-sided p value < 0.05 was considered statistically significant. Geospatial analyses were conducted using ArcGIS, version 10.7.1 (Environmental Service and Research Institute [ESRI], Inc., Redlands, CA, USA). U. S. Census Tiger Cartographic Boundary datasets were used in Figure 1.³¹

Figure 1.

Geographic distribution of outpatients who completed screening colonoscopy. Legend: , University Hospital; , University Hospital outpatients (n = 1495); , East Ann Arbor Health Center; , East Ann Arbor Health Center outpatients (n = 2423); , Northville Health Center; , Northville Health Center outpatients (n = 1171); , all outpatients (n = 5089); , State of Michigan census tract boundaries.

RESULTS

During the study interval, a total of 5919 outpatient-screening colonoscopies were completed, of which 5162 met inclusion criteria and were further analyzed. On examination of patient driving distance, the initial mean distance was 19.6 miles with a standard deviation of 25.8 miles. Further examination of the distribution of driving distance noted 73 patients with a driving distance greater than 3 standard deviations from the mean (from greater than 100 miles, up to 468 miles), which were deemed outliers and thus not included in the final study analysis. Selected patient and procedure characteristics for the remaining 5089 patients are summarized in Table 1. The mean driving distance was 17.2 miles with a median distance of 13.1 miles, which corresponded to a mean travel time of 22.4 min with a median time of 18.5 min. Fifty-four percent of the patients were female. The majority (approximately 80%) of the patient population were of white race, 9% were black, and 7% were Asian. Eighty-one percent of the patient population was privately insured, 13% were Medicare, 5% Medicaid, and a small percentage were insured through the United States Department of Defense Military Health System (TRICARE). The mean number of screening colonoscopies performed per endoscopist was 70.7. Most procedures, approximately 89%, were characterized as having an adequate bowel preparation and 11% were inadequate. Overall, 1884 patients were found to have at least one adenomatous polyp on their colonoscopy, resulting in an adenoma detection rate of 37%.

Table 1.

Demographics and Sample Characteristics

Patients	n = 5089 (%)
Procedure site
East Ann Arbor	2423 (48)
University Hospital	1495 (29)
Northville Health Center	1171 (23)
Driving distance (miles)
Mean (± SD)	17.2 ± 14.1
Median	13.1
Travel time (minutes)
Mean (± SD)	22.4 ± 13.9
Median	18.5
Age (years)
Mean (± SD)	57.4 ± 7.0
Sex
Female	2727 (54)
Race
White	4064 (80)
Black	457 (9)
Asian	357 (7)
Refused/not recorded	80 (2)
Health insurance
Private	4139 (81)
Medicare	686 (13)
Medicaid	238 (5)
TRICARE	22 (0.4)
Endoscopist (n = 72)
Mean procedures (± SD)	70.7 ± 21.5
Procedure timing
Before 12 PM	2509 (49)
After 12 PM	2128 (42)
Not recorded	452 (9)
Bowel preparation
Adequate	4547 (89)
Inadequate	542 (11)
Adenoma detection	1884 (37)

The geographic locations of the three Medical Procures Units and 5089 patient residences are illustrated in Figure 1. Of the total study population, 2423 patients (48%) completed their colonoscopy at the EAA MPU, 1495 patients (29%) at the UH MPU, and 1171 patients (23%) at the NHC MPU. The frequency of outpatients driving distance according to 10-mile intervals is shown in the included histogram. Overall, the histogram was skewed right with 85% of patients having a driving distance to their colonoscopy site of 30 miles or less. Figure 2 illustrates the unadjusted odds ratios for the association of driving distance by 10-mile intervals with adequate bowel preparation. Driving distances of up to 30 miles or less were significantly associated with a greater likelihood of an adequate bowel preparation (odds ratio = 1.37; 95% confidence interval 1.09 to 1.72).

Figure 2.

Odds ratios for an adequate bowel preparation according to driving distance to procedure site. Legend: , odds ratio; , 95% confidence interval.

The time of day that the colonoscopy was performed, before 12 PM or after 12 PM, was not associated with bowel preparation quality or adenoma detection (odds ratio = 1.12, 95% confidence interval 0.93 to 1.36) and (odds ratio = 1.06, 95% confidence interval 0.94 to 1.20) respectively. Table 2 summarizes the results of univariate and multivariable analyses for characteristics associated with adequate bowel preparation. In our adjusted analysis, an adequate bowel preparation was positively associated with female sex (compared to males) and Asian race (compared to white race). Factors that were negatively associated with an adequate bowel preparation included the following: Medicare or Medicaid insurance (compared to private insurance); Black race (compared to white race); undergoing colonoscopy at the NHC MPU (compared to the EAA MPU); and increasing driving distance from a patient’s residence to their colonoscopy procedure site. The factors that were associated with adenoma detection are summarized in Table 3. An adequate bowel preparation and an older age at the time of colonoscopy were associated with a greater likelihood of adenoma detection. Female sex (compared to males) was negatively associated with adenoma detection. Patient race, insurance type, and driving distance from the patient’s residence to their colonoscopy site were not associated with adenoma detection.

Table 2.

Logistic Regression of Predictors for Adequate Bowel Preparation (n = 5089)

Patient characteristics	Univariate analysis Odds ratio (95% CI)	Multivariate analysis Odds ratio (95% CI)
Age (years)	0.98 (0.97–0.99)*	0.99 (0.97–1.00)
Sex (female)	1.20 (1.01–1.44)*	1.22 (1.01–1.47)*
Health insurance	Reference (Private)	Reference (Private)
Medicare	0.55 (0.44–0.70)*	0.60 (0.45–0.80)*
Medicaid	0.47 (0.33–0.66)*	0.48 (0.33–0.71)*
Race	Reference (White)	Reference (White)
Black	0.53 (0.44–0.70)*	0.52 (0.39–0.70)*
Asian	2.17 (1.34–3.52)*	2.32 (1.40–3.84)*
Procedure site	Reference (East Ann Arbor)	Reference (East Ann Arbor)
University Hospital	1.06 (0.85–1.31)	0.85 (0.62–1.16)
Northville Health Center	0.81 (0.65–1.01)	0.69 (0.51–0.95)*
Endoscopist	†	†
Driving distance (10-mile increments)	0.92 (0.87–0.97)*	0.91 (0.85–0.97)*

*p < 0.05. ^†Odds ratios not shown; 72 individual endoscopists were included in the analysis

Table 3.

Logistic Regression of Predictors for Adenoma Detection (n = 5089)

Patient characteristics	Univariate analysis Odds ratio (95% CI)	Multivariate analysis Odds ratio (95% CI)
Age (years)	1.02 (1.01–1.03)*	1.02 (1.01–1.03)*
Sex (female)	0.66 (0.59–0.74)*	0.65 (0.58–0.73)*
Health insurance	Reference (Private)	Reference (Private)
Medicare	1.22 (1.04–1.44)*	1.10 (0.90–1.33)
Medicaid	1.07 (0.82–1.40)	1.19 (0.90–1.58)
Race	Reference (White)	Reference (White)
Black	0.82 (0.66–1.00)	0.83 (0.67–1.03)
Asian	0.85 (0.67–1.06)	0.88 (0.70–1.12)
Procedure site	Reference (East Ann Arbor)	Reference (East Ann Arbor)
University Hospital	0.95 (0.83–1.09)	1.03 (0.84–1.25)
Northville Health Center	1.18 (1.02–1.36)*	1.07 (0.87–1.31)
Endoscopist	†	†
Driving distance (10-mile increments)	1.01 (0.97–1.05)	1.02 (0.98–1.06)
Adequate preparation	1.38 (1.13–1.67)*	1.53 (1.24–1.88)*

*p < 0.05. ^†Odds ratios not shown; 72 individual endoscopists were included in the analysis

DISCUSSION

This study examined the effect of driving distance to screening colonoscopy on the quality of bowel preparation and adenoma detection. In our analysis of 5089 screening colonoscopy procedures performed at Michigan Medicine from January 1, 2017, through December 31, 2017, we found that increasing driving distance to the site of the screening colonoscopy was negatively associated with achieving an adequate bowel preparation. This finding was supported on multivariable analyses after adjusting for patient age, sex, race, insurance, site of procedure, and the endoscopist (odds ratio = 0.91; 95% confidence interval 0.85 to 0.97). This is the first study to our knowledge to investigate this factor, and consequently, to show this effect. Furthermore, the likelihood of an adequate bowel preparation was greater in patients with a driving distance of 30 miles or less (odds ratio = 1.37; 95% confidence interval 1.09 to 1.72). A possible explanation for this observation may be a result of the inverse relationship between the cleanliness of the bowel preparation and the time span between the last dose of bowel preparation and the start of the colonoscopy.¹⁹ Increasing driving distance likely extends the time period between the last dose of preparation consumed and arrival at the location of the screening procedure.

Given the above findings, and the fact that our study and many prior studies have shown that decreased bowel preparation quality is associated with decreased adenoma detection and/or increased miss rates, we anticipated observing a negative association between distance traveled and adenoma detection.^8–11 However, no significant association was observed. Likely explanations for this may be an under-powering to detect this effect due to the smaller size of the patient population with detected adenomas, as well as a relatively small proportion of patients with inadequate bowel preparation (11%). Furthermore, in accordance with past studies, our observed adenoma detection rates differed across endoscopists, and for those performing greater than 50 colonoscopies, individual adenoma detection rates varied from 20% to greater than 50% with a mean of 37.5% and standard deviation of 9.6%.^3,32–37 Finally, on an unadjusted subgroup analysis of the 1884 patients with adenomas, the negative association of driving distance with adequate bowel preparation was again observed (odds ratio = 0.94; 95% confidence interval 0.88 to 0.99). If increasing driving distance negatively effects adenoma detection, we believe it is mediated through decreased bowel preparation quality and would require a larger study sample to fully investigate.

To investigate intra-procedure process measures, a subgroup analysis was conducted on the 4217 colonoscopy procedures where total procedure time and withdrawal time where documented. The mean total procedure time was 23.8 min with standard deviation of 11.9 min. The mean withdrawal time was 14.6 min with standard deviation of 9 min. Greater driving distance was associated with longer total procedure time (p < 0.001), as well as longer withdrawal time (p < 0.001). It is possible that this observed association may also be mediated by the effects of driving distance on patient bowel preparation quality.

The effect of driving distance on bowel preparation is clinically significant due to the large number of screening colonoscopies performed in the USA, which are estimated at greater than 6 million each year.³⁸ If the effect of increased distance resulted in an 8% reduction in adequate bowel preparation as we have observed, this suggests that roughly 480,000 screening procedures annually suffer from suboptimal bowel preparation partly related to greater travel distances. Whether this can be ameliorated in some way will be a topic of future research.

As an observational study, there are several limitations that should be considered when interpreting the study findings. First, the generalizability of the findings may be limited due to the single-site study design. The use of a single site facilitated access to patient residential address data, thereby allowing for geocoding to individual point locations and the subsequent calculation of point-to-point driving distance. Secondly, potential confounders such as medical history and medications that may alter the effectiveness of bowel preparation were not included in this study protocol. We attempted to limit bias related to these factors by including all age-appropriate outpatient screening colonoscopies in the study sample. Thirdly, the patient’s residential address may not represent the actual location of where they completed their bowel purgative. For example, patients who live a great distance may choose to complete their bowel preparation in a hotel or other accommodation that is in greater proximity to their procedure site. This is likely the explanation for the seventy-three patients who were excluded from the final analysis as their residential addresses were located greater than 100 miles, to as far as 480 miles, from the site of their colonoscopy. Lastly, unobserved variables that are not routinely collected during standard care such as patient education, income, motivation, and alternative modes of transportation may also have a significant impact on colonoscopy quality measures.

Despite the above limitations, we believe the findings of our study suggest the possibility of a negative impact of distance traveled on bowel preparation quality and leave unanswered the question of the potential impact of distance traveled on adenoma detection. The impact on bowel preparation highlights a potential need to mitigate this factor, if we are to increase the likelihood of achieving high-quality screening examinations among all patient populations. An obvious solution may be to focus resources on increasing access by making endoscopy more accessible outside of urban and suburban areas, but the reality of such a proposal is questionable given the high resource needs inherent to endoscopy from both a standpoint of infrastructure (procedural rooms, preparation and recovery space, emergency equipment) and human resources (nurses, technicians, anesthesiologists, endoscopists).³⁹ Additional possibilities may also include alternative pre-procedure recommendations targeting patients traveling greater than 30 miles such as the following: alternative preparation guidelines, pre-procedural travel coordination to enable local stay, or adjustment in procedural timing to enable increased ability for split-prep coordination.

Future prospective research will be vital in reproducing the findings of this study and to thoroughly characterize populations who travel long distances for screening colonoscopy to better understand reasons for length of travel, to identify additional factors outside of resource availability that may contribute to this decision, and to better understand if long-distance travelers are inherently different from short-distance travelers.

Compliance with ethical standards

Conflict of Interest

The authors declare that they do not have a conflict of interest.