Since Capsule endoscopy (CE) was introduced in 2000, it has been widely used as the main tool for diagnosing small bowel diseases [1]. Although CE is useful for diagnosing small bowel diseases, it has some limitations including incomplete examinations and capsule retention [2-4]. Occasionally, capsules cannot reach the cecum due to various causes, thus leading to incomplete examination of the small bowel. Another problem is capsule retention. Most patients in whom capsule retention occurs are asymptomatic; however, some require surgical or enteroscopic capsule removal [4-9]. The clinical performance and complications of small bowel CE include completion rate, capsule retention rate, and indications [2,3]; these have also been described in Korea [10]. This study aimed to investigate the clinical performance and complications of small bowel CE based on 17-year data from a Korean Capsule Endoscopy Registry. Furthermore, recent changes in the clinical performance and complications of small bowel CE were also evaluated.

CE registry data from 35 hospitals, collected between October 2002 and April 2019, were retrospectively analyzed. Clinical information, including demographic data, completion rate, capsule retention rate, indications, CE diagnosis, and bowel preparation data, was collected and analyzed. From September 2014, health insurance benefits were provided to patients with obscure gastrointestinal bleeding (OGIB) in Korea. However, for patients with small bowel tumor(s), Crohn’s disease, and other small bowel diseases, a patient burden of 80% was applied. As such, data from the most recent 5 years (September 2014 to April 2019) were compared with those from the previous 12 years (October 2002 to August 2014).

Indications for CE included OGIB, abdominal pain, chronic diarrhea, small bowel tumor(s), Crohn’s disease, weight loss, protein-losing enteropathy, and screening. OGIB was defined as bleeding of unknown cause that persisted or recurred after initial upper gastrointestinal endoscopy and colonoscopy with negative results [11,12]. In addition to overt bleeding (melena or hematochezia), occult bleeding (persistent iron deficiency anemia or positive stool occult blood) was also considered OGIB [12,13].

Before CE examinations, patients were offered a bowel preparation regimen according to clinician preferences. Options for the bowel preparation included nil per os (NPO), polyethylene glycol (PEG), PEG + ascorbic acid, sodium phosphate (NaP), picosulfate, or others. Bowel preparation quality was categorized by independent examiners as follows: excellent, ≥ 75% of the mucosa visualized; good, 50% to 74% of the mucosa visualized; fair, 25% to 49% of the mucosa visualized; poor, ≤ 24% of the mucosa visualized [14]. For the purpose of study analysis, excellent or good bowel preparation were deemed adequate, and fair or poor preparation were deemed inadequate [15]. Comparison was performed between adequate and inadequate bowel preparation quality.

CE diagnoses were based on CE structured terminology. Complete examination was defined when the capsule reached the cecum during the recording time [2,3]. Capsule retention was defined when the capsule remained in the digestive tract for > 2 weeks [2,10]. Completion and capsule retention rates were calculated, and risk factors affecting incomplete examination and capsule retention were also investigated. Acquisition of informed consent was exempted and the study design was approved by the Institutional Review Board of Seoul Metropolitan Government Seoul National University Boramae Medical Center (approval number: 20190802/10-2019-62/091).

Data are expressed as mean ± standard deviation (SD) for continuous variables and number (%) for categorical variables. Risk factors for incomplete examination and capsule retention were analyzed using logistic regression models. Statistical analysis was performed using SPSS version 20.0 (IBM Corporation, Armonk, NY, USA).

In this registry-based study including 4,650 CE examinations, the incomplete examination and capsule retention rates were determined. This study revealed an incomplete examination rate of 16%, which is similar to that reported in previous studies [2,3]. The capsule retention rate was 3%, which is slightly higher than that reported in previous studies [2,3]. The incomplete examination rate of recent CE (September 2014 to April 2019) decreased compared with that of previous CE (October 2002 to August 2014). With the extended battery life of newer CE technologies, more capsules have reached the ileocecal valve and cecum, leading to a decrease in the number of incomplete examinations [16,17]. With technical advances in radiological examinations, such as computed tomography enterography and magnetic resonance enterography, more patients with small bowel stricture(s) can be diagnosed before undergoing CE. However, the decrease in capsule retention rate over time was not statistically significant in our study. Moreover, our data lacked radiological examination results and, thus, analysis in this regard was not possible. The most common indication for CE was OGIB (64.4%), which is consistent with results reported in previous studies [2,3,10]. In our study, recent CE examinations had more OGIB indications than previous CE examinations (p < 0.001), which can be explained by the inception of health insurance coverage for patients with OGIB in September 2014.

Recently, the incidence of Crohn’s disease has been found to be increasing in Korea [18]. Our study revealed a recent increasing tendency of indications and CE diagnosis of Crohn’s disease. CE diagnosis of NSAID enteropathy demonstrated an increasing tendency without statistical significance. The increase in NSAID enteropathy can be attributed to the aging population. In our study, the proportion of normal results was smaller in recent CE examinations than in previous examinations. Recent advances in CE technology with improved resolution may have led to more lesion detection and fewer patients diagnosed with normal findings.

Our study revealed that factors associated with incomplete examination were inadequate bowel preparation and indications other than OGIB, which is consistent with the results of a previous study [10]. With adequate bowel preparation, CE is more likely to be completed. Blood materials in patients with gastrointestinal bleeding appear to act as laxatives, thus helping the capsule proceed through the ileocecal valve. In our study, inadequate bowel preparation was significantly associated with capsule retention, which is also consistent with the results of previous studies [2,10]. The presence of stenotic portions in the small bowel may lead to both inadequate bowel preparation and capsule retention. Additionally, fecal materials stuck in the stenotic portion may result in capsule retention. Although causality was difficult to determine, our study revealed that inadequate bowel preparation was significantly associated with capsule retention. Crohn’s disease was a risk factor for capsule retention and the capsule retention rate was the highest among patients with the indication of Crohn’s disease. Special caution or using a patency capsule will be needed in patients with Crohn’s disease.

In this study, bowel preparation quality was affected by the bowel preparation regimen. PEG 4 L or NaP more favorably affected bowel preparation than NPO; however, PEG + ascorbic acid resulted in worse bowel preparation than NPO. In our study, the recent data revealed that PEG + ascorbic acid regimen was the most widely used. This can be explained by the fact that recent guidelines recommend that CE should be performed as soon as possible (generally after colonoscopy) in patients with overt, obscure bleeding [11], and PEG + ascorbic acid has recently become the most popular regimen for colonoscopy in Korea [19]. The time interval from the ingestion of the bowel preparation regimen to performing CE can be delayed because performing colonoscopy and clinician’s decision-making to perform CE after colonoscopy can take time. This time delay may adversely affect bowel preparation quality [20,21], because debris and intestinal fluid can affect preparation of the distal small bowel [22].

Our study had some limitations, the first of which was its retrospective design and, as such, may have been susceptible to selection bias. Moreover, our data may have been susceptible to the under-reporting of complications. Second, our investigation was a multi-center, registry-based study, and the data collection methods used at each institution were not monitored. There was no auditing system to control data collection. However, this was a large study based on 17-year registry data. Time trends were also investigated between recent and previous data.

In conclusion, our 17-year data suggest that CE is a useful and safe tool for diagnosing small bowel diseases. The incomplete examination rate of CE decreased with time and OGIB was consistently the primary indication for CE. Inadequate bowel preparation was significantly associated with capsule retention and incomplete examination.