Unlocking the colon clock: Bridging the gap in colonic transit time studies for optimal management of chronic constipation

Abstract

Functional constipation affects up to 15% of the global population, significantly affecting the quality of life and imposing substantial clinical and economic burdens. Colonic transit time (CTT) studies have emerged as a pivotal diagnostic tool for distinguishing various types of functional constipation (i.e., slow transit constipation, normal transit constipation, and ano-rectal dyssynergia), thereby guiding personalized treatment strategies and enabling precise monitoring of therapeutic response. CTT studies using radiopaque markers (ROM) have been the most widely used technique by researchers worldwide. Despite its affordability and high diagnostic yield, the ROM CTT study remains grossly underutilized in routine clinical practice largely due to a pervasive lack of awareness among physicians regarding its methodological nuances and clinical advantages. This narrative review systematically examined the multifaceted role of ROM CTT studies in clinical practice. It underscored how ethnic, dietary, and lifestyle factors profoundly influence colonic motility, thereby necessitating the development of population-specific diagnostic protocols. The review also highlighted the significant variability in imaging methodologies, such as differences in radiographic timing and patient positioning (supine vs erect), which further complicate the interpretation and reliability of CTT assessments. By drawing on a wide spectrum of research, this review advocated for enhanced physician education and the implementation of standardized, evidence-based protocols. Such initiatives are critical to optimizing the diagnostic accuracy and clinical utility of ROM CTT studies, ultimately leading to more effective management of refractory constipation and improved patient outcomes.

Key Words: Constipation; Gastrointestinal motility; Colonic transit time; Abdominal radiography; Diagnostic techniques; Digestive system; Ethnic groups; Health care disparities

Core Tip: Colonic transit time (CTT) assessment using radiopaque markers (ROM) is a cost-effective, underutilized tool for subtyping functional constipation and guiding therapy. This review highlighted the need for standardized ROM CTT protocols tailored to regional transit characteristics, especially in Asian populations. It underscored the importance of multicentric normative data, clinician awareness, and technological innovations like artificial intelligence-assisted marker analysis to elevate the ROM CTT study from a research tool to a routine diagnostic modality.

INTRODUCTION

Chronic constipation is a common gastrointestinal disorder affecting up to 15% of the population. It is broadly classified as either primary (functional) or secondary, depending on the underlying cause[1-4]. Chronic constipation exerts a profound impact on patient quality of life, contributing to psychological distress, social withdrawal, and diminished work productivity[1,2,5-7]. The burden of constipation extends beyond the individual, resulting in substantial healthcare utilization and economic costs due to frequent physician visits and diagnostic evaluations, as well as chronic pharmacotherapy. Moreover, functional constipation (FC) commonly overlaps with other disorders of gut-brain interaction and can be misdiagnosed or overlooked[8]. Despite its high prevalence, constipation is often under-recognized and undertreated, especially in resource-limited settings.

The pathophysiology of FC is multifactorial[9]. The Rome IV criteria provide a standardized framework for diagnosing FC, requiring at least two of the following symptoms for at least 3 months (with onset at least 6 months prior): (1) Straining during more than 25% of defecations; (2) Lumpy or hard stools in more than 25% of defecations; (3) Sensation of incomplete evacuation in more than 25% of defecations; (4) Sensation of anorectal obstruction or blockage in more than 25% of defecations; (5) Manual maneuvers to facilitate more than 25% of defecations (such as digital evacuation or support of the pelvic floor); and (6) Fewer than three spontaneous bowel movements per week. Additionally, there should be the absence of alarm features (unintentional weight loss, cachexia, age > 50 years, new-onset altered bowel habits, blood in stools, unexplained iron deficiency anemia, etc.), loose stools should rarely be present without the use of laxatives, and there should be insufficient criteria for irritable bowel syndrome[10,11].

The initial evaluation should exclude secondary causes, such as metabolic and neurological disorders or side effects of medications. Therefore, history, physical examination, and basic laboratory tests are important (Figure 1). Colonoscopy is reserved for patients with alarm features. First-line therapy for most patients includes lifestyle and dietary modifications, such as increasing fiber and fluid intake, regular exercise, and proper toilet habits, followed by laxatives. Patients who fail to respond to empirical management or who present with atypical features need assessment of colonic transit and anorectal function testing. Colonic transit time (CTT) measurement has emerged as a pivotal, objective tool for evaluating cases with refractory constipation. By objectively quantifying transit time, CTT studies enable clinicians to tailor interventions, such as prokinetics/secretagogues for slow transit constipation (STC) or biofeedback therapy for dyssynergic defecation (DD), thereby optimizing outcomes. Despite its established utility, CTT assessment remains underutilized in many regions, likely due to limited awareness, lack of availability, and lack of standardized protocols[12-14].

Figure 1 Diagnostic approach for evaluating chronic constipation. PEG: Polyethylene glycol; MOM: Milk of magnesia; FED: Fecal evacuation disorder; CTT: Colonic transit time; ARM: Anorectal manometry; BET: Balloon expulsion test; IBAT: Ileal bile acid transporter; IBS-C: Irritable bowel syndrome-constipation.

Notably, there are significant ethnic and dietary differences in gut motility, with Asian populations demonstrating faster colonic transit than Western cohorts[12]. These differences underscore the need for region-specific reference values and protocol adaptations to ensure accurate diagnosis and management. This review explores the clinical relevance, diagnostic methods, and ethnic variability in the radiopaque markers (ROM) study used to assess CTT while highlighting methodological challenges and gaps in knowledge.

CLASSIFICATION OF FUNCTIONAL CONSTIPATION

Primary or FC is further divided into three pathophysiological subtypes with distinct pathophysiologies: Normal transit constipation (NTC), STC, and DD[14]. These subtypes are distinguished by differences in colonic transit and anorectal function, which helps in guiding management[15]. In NTC, patients experience symptoms of constipation despite having normal colonic transit and defecatory function. This often results from psychosocial factors, visceral hypersensitivity, or lifestyle influences. NTC typically responds well to first-line measures such as increased dietary fiber, fluid intake, physical activity, and behavioral interventions.

STC is characterized by reduced colonic motility and prolonged CTT. Patients with STC often have infrequent bowel movements associated with diminished frequency and high-amplitude propagating contractions. Management of STC includes dietary modifications and drugs to improve CTT. DD results from impaired coordination of the pelvic floor and anal sphincter muscles during defecation, leading to functional outlet obstruction. Diagnosis of DD relies on anorectal manometry, balloon expulsion, and/or defecography[16-19]. DD may coexist with other constipation subtypes, especially STC, complicating the clinical picture. The gold standard for treatment is biofeedback therapy, which retrains pelvic floor muscles and improves defecatory coordination. Standard laxatives are generally ineffective for DD. Recent guidelines have emphasized individualized management based on constipation subtype[20]. Overlap between subtypes is common, and patients may transition between categories over time, requiring periodic reassessment and adjustment of therapy. Long-term management should remain flexible with a focus on improving quality of life and symptom control.

COLONIC MOTILITY AND TRANSIT TIME

Colonic motility is a critical process underlying the major functions of the large bowel, such as storage, absorption, propulsion, and defecation[21]. Disorders of colonic motility typically present with constipation or diarrhea. Multiple factors may significantly influence CTT, and understanding these variables is helpful for accurate assessment and management of constipation across diverse populations. Studies have demonstrated that Asian populations tend to have shorter mean CTT than their Western counterparts[22]. Mean CTT in healthy Indian, Korean, and Hong Kong Chinese adults has been reported to be 15.4 hours, 16.8 hours, and 24.5 hours, respectively. In contrast, Western populations typically exhibit a mean CTT of 30-40 hours[23,24]. These marked differences are largely attributed to dietary habits, particularly the higher intake of dietary fiber in Asian diets. Traditional East Asian diets are rich in whole grains, legumes, vegetables, and fruits, all of which contribute to increased stool bulk and more rapid CTT. Vegetarianism, which is prevalent in many regions of Asia, further enhances fiber intake and may explain the shorter CTT observed in these populations[22-26].

Anatomical differences in colonic configuration - particularly a redundant or elongated colon - can significantly slow colonic transit and predispose patients to chronic refractory constipation[27]. A redundant sigmoid colon (dolichosigmoid) increases the length and tortuosity of the bowel, thereby prolonging the time for fecal matter to traverse the colon. Recent studies have confirmed that individuals with infrequent bowel habits tend to have longer colonic length, as revealed on imaging[27,28]. For example, a CT colonography study demonstrated that patients with constipation (defined by low defecation frequency) had a significantly longer colon, especially a lengthened proximal colon, compared to those with daily bowel movements[28]. Transit time has also been shown to rise in proportion to the number of redundant loops present[27]. Clinically, these anatomical variations manifest as bloating, abdominal discomfort, and decreased stool frequency associated with slow transit. Importantly, imaging modalities such as barium enema or computed tomography colonography can delineate a dolichocolon, particularly redundancy of the sigmoid segment, as the structural contributor to constipation[27].

Fluid intake is another variable that can influence CTT. Adequate hydration is essential for maintaining stool softness and promoting efficient transit, and populations with higher average fluid intake may experience shorter CTTs[25]. Meal timing and frequency also play a role; irregular meal patterns or frequent snacking, as seen in some urban populations, may disrupt normal colonic motility. The use of traditional spices and herbal remedies, common in Asian cuisines, may have additional modulatory effects on gastrointestinal function, although robust data on their impact on CTT are limited.

Cultural and lifestyle practices also play a significant role in modulating CTT[29]. In several Asian countries, the practice of early morning defecation is a well-established cultural norm often reinforced from childhood. This habit is believed to promote regular bowel movements and may contribute to faster CTT. Additionally, the use of traditional squatting toilets in many Asian countries, as opposed to Western-style sitting toilets, has been associated with more complete and efficient evacuation, potentially reducing CTT. Demographic factors such as age and sex further contribute to variability in CTT[30,31]. Females generally have longer CTT than males - effects of progesterone during the menstrual cycle and pregnancy. Aging is associated with a gradual slowing of CTT. Socioeconomic status and occupational patterns may also play a role; individuals from lower socioeconomic backgrounds or those engaged in physically demanding occupations may have different transit profiles compared with more affluent or sedentary groups. Beyond diet and ethnicity, patient-specific factors such as age and comorbid conditions (e.g., diabetes or neurologic disease) markedly influence CTT.

Advancing age is generally associated with a gradual slowing of colonic motility. Healthy older adults may have CTTs comparable to those of younger individuals[32], but in the presence of frailty or illness, transit can be substantially delayed. Indeed, studies of constipated nursing-home residents and other older patients report total gut transit times of 4-9 days (far exceeding the normal < 3 days)[32]. Contributing factors include age-related degeneration of the enteric nervous system, reduced physical activity, and polypharmacy (many elderly patients take medications such as opioids or anticholinergics that impair motility).

Chronic diabetes is well known to affect gastrointestinal motility via autonomic neuropathy. Diabetic constipation often manifests as slow colonic transit: One comparative study found that diabetic patients had a significantly longer mean CTT (approximately 35 hours) than healthy controls (approximately 20 hours)[33]. Notably, diabetic patients who met clinical criteria for constipation showed especially prolonged transit in the left colon and rectosigmoid regions, consistent with impaired propagating contractions in the distal gut. However, even diabetics without overt constipation symptoms may have subclinical transit delays. Recent evidence from wireless motility capsule studies has indicated that overall gut transit is slower in diabetes (both type 1 and 2) as compared to non-diabetics, regardless of whether the patient perceives themselves as constipated[34,35]. This suggests that diabetes-related neuropathy can globally dampen gastrointestinal motility, and symptoms may only become apparent when additional factors (e.g., diet, medications, etc.) tip the balance.

Neurologic injury is another key factor. Up to half of stroke survivors experience constipation due to a combination of immobility, neurogenic bowel dysfunction, and medications such as the calcium-channel blockers or opiates used post-stroke[36]. Colonic transit studies in post-stroke patients confirm a significant slowdown in those with clinical constipation. In one study, stroke patients with constipation had a mean total colonic transit of approximately 47 hours, markedly longer than the approximately 32 hours in stroke patients without constipation (who more closely approximated normal transit)[36]. The prolonged transit in stroke-related constipation is often accompanied by impaired coordination of colonic contractions and pelvic floor dysfunction due to central nervous system injury. Given the multifactorial nature of CTT variability, it is clear that region-specific and population-specific normative values are essential for accurate diagnosis of slow CTT. Applying Western reference standards to Asian or other non-Western populations may lead to misclassification and inappropriate treatment. Therefore, physicians should consider the broad spectrum of ethnic, dietary, lifestyle, and demographic variables when interpreting CTT results and formulating management plans.

CTT MEASUREMENT: TECHNIQUES AND CHALLENGES

Measurement of CTT is an important step in the evaluation of refractory constipation. In addition to objectively diagnosing the subtype of FC, CTT allows quantification of the severity of the problem and aids in assessing the response to treatment. Various techniques available for CTT measurement include a ROM study, wireless motility capsule, and scintigraphy. Wireless motility capsule technology offers a non-radiological alternative, measuring pH, pressure, and temperature as the capsule traverses the gastrointestinal tract. Scintigraphy involves tracking a radiolabeled meal with serial imaging at 24 hours, 48 hours, and 72 hours and calculating the geometric center of radioactivity. Both methods provide comprehensive motility assessment (segmental transit) but are constrained by cost, need for advanced technology, and limited availability[37,38]. In this review, the discussion will be limited to the ROM CTT study.

The ROM study is the most widely used and validated method for assessing CTT, particularly in resource-limited settings. It is simple, inexpensive, reliable, and reproducible, but requires good patient compliance for careful protocol adaptation and exposes patients to some radiation. Additionally, ROM studies can be performed in a variety of clinical settings and do not require highly specialized equipment, making them suitable for use in both urban and rural healthcare facilities. However, the interpretation of ROM results can be influenced by patient compliance, dietary habits, and variations in marker ingestion protocols.

First described by Hinton et al[13] in 1969, this technique involves ingestion of ROM followed by abdominal radiographs to track their progression through the colon. The protocols for CTT studies demonstrate marked variability across populations and research settings, differing substantially in marker number, ingestion schedule, and imaging intervals (Table 1). Marker quantities range from 20-50 per day, reflecting differences in protocol design and the need to balance marker visibility with patient compliance. X-ray timing also varied substantially, from as early as 27 hours after marker ingestion in some studies to as late as 11 days in others, underscoring the influence of local clinical practice and patient characteristics on study design. Several other studies adapted their diagnostic protocols to address the unique needs of subgroups, such as pediatric patients or individuals with neurogenic disorders, highlighting the necessity for tailored approaches in CTT assessment[39,40]. Traditional Western protocols employed ingestion of 20 markers at 0 hour, 24 hours, and 48 hours, with X-ray assessment made at 72 hours[13,34-36].

Table 1 Segmental and total colonic transit time using radiopaque markers across populations and protocols.

Ref.	Sample size/population	Marker ingestion protocol	X-ray timing/type	Key findings	Results (mean CTT or segment analysis)
Arhan et al[41], 1981	23 children, 38 adults	20 markers at 0 hour	Daily until marker clearance	Children show rectosigmoid stagnation	Children: Right 7.7 hours; left 8.7 hours; rectum 12.4 hours; adults: Right 13.8 hours; left 14.1 hours; rectum 11 hours
Metcalf et al[12], 1987	73 controls (group I: 24; group II: 49)	20 markers at 0 hour, 24 hours, 48 hours	Group I: 24 hours, 48 hours, 72 hours; group II: 72 hours	Validated single-film technique	Segmental: Right 11.3 ± 1.1 hours; left 11.4 ± 1.4 hours; rectosigmoid 12.4 ± 1.1 hours
Nabar et al[42], 1995	25 NUD patients, 25 controls	20 markers at 0 hour, 9 hours, 18 hours	27 hours	Altered motility in patients with NUD who were asymptomatic	NUD: 9.0 hours; controls: 15.8 hours
Pai et al[51], 1999	20 healthy males	Markers at 0 hour, 12 hours, 24 hours	12 hours and 36 hours	Two X-rays improved the accuracy in the rapid transit populations	Mean CTT: 24.2 ± 6.8 hours
Ghoshal et al[14], 2007	31 total (9 HD; 11 CIPO; 11 controls)	Markers at 0 hour, 12 hours, 24 hours	36 hours and 60 hours (erect)	60 hours of X-ray is better for HD/CIPO diagnosis	HD/CIPO showed increased retention (HD: Distal; CIPO: Proximal)
Pomerri et al[23], 2007	159 patients with FC (group I: 52; group II: 107)	Group I: 10 markers/day for 10 days; group II: + barium paste on day 9	Day 11 (supine)	Barium paste showed no clinical impact	Group I: 85.75 ± 46.08 hours; group II: 74.94 ± 49.34 hours (NSD)
Abrahamsson et al[52], 2010	15 controls, 13 patients with FC	50 particles/day for 6 days	Day 7	Validated marker quantity requirements	Proposed 10-12 markers/day for accuracy
Cho et al[26], 2013	47 healthy adults (24 F; 23 M)	20 markers/day for 3 days	Day 4 (supine)	Significant sex differences in CTT	Males: 8.8 hours; females: 24.7 hours
Bhate et al[43], 2015	50 patients with FC, 25 controls	4 gelatin capsules (5 markers each) at 0 hour, 12 hours, 24 hours	36 hours (single X-ray)	Right colon transit is slower in FC vs controls	FC: 23.0 hours; controls: 15.4 hours

CTT: Colonic transit time; NUD: Non-ulcer dyspepsia; HD: Hirschsprung’s disease; CIPO: Chronic intestinal pseudo-obstruction; NSD: No significant difference; F: Female; FC: Functional constipation; M: Male.

However, these Western protocols often fail to capture meaningful ROM retention in Asian populations due to their characteristically rapid transit times. As a result, Indian researchers have adapted protocols to better suit local physiology. For instance, Ghoshal et al[40] administered 20 ROM at 0 hour, 12 hours, and 24 hours with radiographs at 36 hours and 60 hours, finding that retention of ≥ 30 markers at 36 hours and ≥ 14 markers at 60 hours provided high sensitivity and specificity for detecting STC or DD. These adaptations highlight the necessity of tailoring protocols to the population under study, considering differences in diet, bowel habits, and baseline transit times (Figure 2A).

Figure 2 The X-ray. A: Plain abdominal radiograph for colonic transit time assessment using radiopaque markers. Three lines need to be drawn to divide the colon into three segments: A vertical line up to the middle of the body of the fifth lumbar vertebra, a line from the body of the fifth lumbar vertebra to the right pelvic outlet, and a line from the fifth lumbar vertebra to the anterior superior iliac crest on the left. These lines divide the colon into three segments: The right colon, left colon, and rectosigmoid (RS) colon. This distribution helps localize segmental delays in colonic transit and differentiates between normal transit, slow transit constipation, and RS outlet dysfunction; B: Comparison of supine (left) and erect (right) abdominal radiographs in a patient undergoing colonic transit time evaluation using radiopaque markers. Although the erect X-ray suggested accumulation of markers in the RS region, the supine film revealed that many markers presumed to be in the RS have shifted from the transverse colon and should be reassigned to the right and left colon. This discrepancy illustrates how gravity-dependent descent of the transverse colon in the erect position can lead to misclassification of marker location and result in a false diagnosis of pelvic floor dysfunction. In this case correct interpretation supports a diagnosis of slow transit constipation. Additionally, accumulation of markers in the cecal region may be erroneously attributed to the RS segment, further emphasizing the importance of anatomical correlation in marker assignment. Rt: Right; Lt: Left; RS: Rectosigmoid.

Imaging technique selection is an essential determinant of ROM CTT study assessment. Despite the widespread use of abdominal radiography as the standard imaging modality in these studies, there remains a lack of consensus regarding the number and type (supine or erect) of abdominal radiographs to be performed at a particular time frame. This methodological variability introduces potential discrepancies in the interpretation of marker distribution, which can directly impact the diagnostic conclusion. When abdominal radiographs are obtained in the erect position, the gravitational influence on the transverse colon may lead to its downward displacement into the pelvic region[41-43]. This anatomical shift can result in the erroneous localization of ROMs, creating a false impression of marker retention in the rectosigmoid region and consequently leading to an incorrect diagnosis of functional outlet obstruction (Figure 2B). To mitigate these limitations, a single abdominal radiograph taken in the supine position is preferable because it results in a lower radiation dose and better interpretation compared with the erect position radiograph[1,15,26,44].

The choice between single vs multiple capsule techniques also introduces methodological complexity. Single-capsule protocols are straightforward but may not be sensitive enough for populations with rapid transit, while multiple capsule protocols involving ingestion on consecutive days and multiple X-rays provide more segmental data but increase radiation exposure. Furthermore, technical issues such as marker clumping, especially in the rectosigmoid region, can lead to overestimation of segmental delay, and segmentation errors can further skew the interpretation[42,43]. Patient compliance is another key factor; adherence to ingestion schedules and radiograph appointments is essential for reliable results[45,46]. Systematic errors may arise if patients deviate from the protocol, such as missing doses or delaying imaging, which can lead to inaccurate estimation of CTT. Finally, mathematical models used to estimate CTT, such as those assuming steady-state transit, may be subject to error, particularly in patients at the extremes of transit speed. Hence, the clinical utility of CTT studies is contingent upon meticulous standardization of methodology, appropriate selection of imaging techniques, and consideration of population-specific variations in gut transit dynamics. Adoption of a single supine abdominal radiograph as the standardized imaging protocol, along with regionally validated marker ingestion schedules, represents a decisive step toward improving the accuracy and reproducibility of colonic transit assessments.

STC must be distinguished from colonic pseudo-obstruction, as the clinical management diverges significantly. While both conditions feature profound colonic dysmotility, their presentations and underlying pathophysiologies differ. Colonic pseudo-obstruction (which can be acute or chronic, such as chronic intestinal pseudo-obstruction) mimics a true mechanical obstruction despite the absence of any luminal lesion. Patients with pseudo-obstruction often present with more severe distension, abdominal pain, and even nausea/vomiting due to pronounced stool and gas accumulation[47]. Objective testing reinforces this distinction: A ROM transit study in STC will show a global slowdown of marker progression through the colon, whereas in chronic intestinal pseudo-obstruction, there may be segments of complete stasis and dramatic colonic dilation on imaging. Moreover, small-bowel manometry or transit scintigraphy can reveal “florid” abnormalities in pseudo-obstruction, reflecting diffuse gastrointestinal dysmotility, which are typically absent in isolated slow-transit constipation. A redundant sigmoid colon can be a confounding factor, since its radiographic appearance may suggest an obstruction; however, a redundant colon generally indicates an anatomical variant associated with STC rather than true pseudo-obstruction[47]. Careful radiologic evaluation (including ruling out torsion of a redundant sigmoid) helps avoid misdiagnosis. In practice, differentiating STC from pseudo-obstruction guides management; true colonic pseudo-obstruction may necessitate urgent decompression, prokinetic therapy (e.g., neostigmine) or even surgery, whereas STC can be managed with conservative measures or elective surgery (i.e., subtotal colectomy) in refractory cases.

CLINICAL APPLICATIONS AND ALGORITHMIC ROLE OF CTT

The CTT study remains a vital diagnostic tool for assessing refractory FC. In the diagnostic algorithm for FC, CTT assessment is best positioned after the initial empirical management with laxatives, dietary fiber, etc., has failed and before consideration of invasive or surgical therapies (Figure 1). By objectively differentiating between NTC, STC, and DD, the CTT study helps to decide the choice of therapeutic interventions. Patients with NTC or STC may benefit from the addition of prokinetic agents, secretagogues, or stimulant laxatives, while those with evidence of DD require targeted biofeedback therapy[6,10,48-50]. Furthermore, CTT studies can help distinguish DD from clinically misdiagnosed irritable bowel syndrome with constipation, as the latter often presents with normal transit despite prominent symptoms. This distinction is the key, as it prevents unnecessary escalation of therapy and facilitates appropriate management. The CTT study may also be performed after excluding DD through anorectal function testing (by anorectal manometry, defecography, and rectal balloon expulsion test). Additionally, the CTT study may help to diagnose coexisting STC in cases diagnosed with DD by other techniques and who continue to exhibit symptoms despite treatment for defecatory disorders. A CTT study is also valuable in monitoring therapeutic efficacy. The improvement in transit time after intervention can provide objective evidence of treatment response, supporting decisions to continue or escalate therapy[51,52].

GAPS IN LITERATURE AND UNDERUTILIZATION OF CTT STUDIES

Despite the high prevalence of FC, the utilization of ROM CTT measurement remains suboptimal, which suggests several persistent gaps in the literature and healthcare practice. A major barrier is limited awareness among physicians regarding the indications, protocols, and interpretation of ROM CTT studies. This knowledge gap contributes to the underuse of the tests, thereby resulting in misclassification of constipation subtypes and inappropriate therapy. The literature on ROM CTT is characterized by a paucity of large, multicentric studies comparing healthy and constipated cohorts using standardized protocols. Most available data are derived from single-center studies with limited sample sizes, restricting the generalizability of findings and the establishment of robust normative values. Furthermore, there is a lack of consensus on the optimal protocol for ROM CTT measurement in Asian patients, with various centers employing different marker types, ingestion schedules, and radiograph timings. This heterogeneity hampers the development of regional/national guidelines and complicates the interpretation of results across different settings. The global literature on ROM CTT assessment is skewed toward single-center, small-sample studies and lacks well-powered, multicenter investigations, particularly in Asian populations, using standardized protocols. Western studies, such as that by Metcalf et al[12], have long-established normative CTT values and validated segmental analysis using ROMs, but these benchmarks may not be applicable to populations with inherently faster gut transit.

Asian researchers, including those in China, Korea, and India, have also contributed to understanding CTT physiology in their regions. In a pivotal Korean study, Kim et al[21] demonstrated a mean total CTT of approximately 24-30 hours among healthy adults with segmental transit times of 6-13 hours depending on colonic region and sex. Another Korean study by Jung et al[33] showed that females had significantly longer total CTTs than males and proposed sex-specific normative data. In a study of Chinese adults Cho et al[26] found a similar trend of faster transit compared with Western populations, suggesting the need for population-specific reference standards. An Indian study by Ghoshal et al[40] reported a mean CTT of 15 hours in healthy controls and demonstrated high diagnostic accuracy at the 60-hour radiograph for detecting motility disorders. Nabar et al[42] and Bhate et al[43] further validated these findings, emphasizing the importance of segmental transit assessment. However, these studies were limited by small sample sizes and a lack of multicentric design. Collectively, these studies highlighted significant inter-individual and inter-group variability in CTT among different populations and reinforced the need for region-specific normative data and standardized protocols. However, despite these important contributions, research in this field remains fragmented, and there is a need for large-scale, guideline-driven studies to harmonize CTT assessment and interpretation across different populations.

Several practical barriers continue to limit the widespread adoption of CTT studies in clinical practice. In rural and resource-limited settings, the lack of access to ROMs and radiographic facilities remains a significant challenge, often preventing clinicians from performing these assessments. Concerns about radiation exposure also affect decision-making. Also, there is a proven lack of awareness about the testing. To address these issues, we need to prioritize targeted educational initiatives for healthcare providers, invest in diagnostic infrastructure, and develop streamlined, cost-effective protocols that are practical for use across diverse clinical populations.

RECOMMENDATIONS AND FUTURE DIRECTIONS

To address the current limitations and unlock the full potential of ROM CTT measurement in the Asian context, several strategic recommendations can be proposed. First, there is a pressing need to adopt a simplified and standardized ROM CTT protocol that is validated for Asian populations. Such a protocol should account for local dietary habits, cultural practices, and baseline transit characteristics while minimizing radiation exposure and logistical complexity. Second, the establishment of multicentric normative data is essential for defining accurate cutoff values and enhancing the diagnostic precision of ROM CTT studies. Collaborative research across diverse Asian populations will facilitate the development of robust reference intervals and comparisons across regions and countries. Third, the integration of CTT assessment into postgraduate training curricula and continuing medical education programs is critical for raising awareness and building expertise among clinicians. Educational initiatives should emphasize the indications, protocols, and interpretation of CTT as well as its role in the broader diagnostic algorithm for chronic constipation. Fourth, technological innovation holds significant promise for enhancing the accessibility and accuracy of CTT measurement. The application of artificial intelligence (AI) and machine learning algorithms to radiograph interpretation can automate marker counting, reduce inter-observer variability, and streamline workflow in busy clinical settings. Pilot studies exploring AI-based solutions should be encouraged with the goal of developing user-friendly tools that can be deployed in both urban and rural healthcare environments. Finally, ongoing research should focus on evaluating the clinical impact of CTT-guided management strategies, assessing cost-effectiveness, and exploring novel protocols that limit patient inconvenience and radiation exposure. By prioritizing these recommendations, the gastroenterology community can ensure that ROM CTT measurement becomes a cornerstone of evidence-based constipation management.

CONCLUSION

CTT measurement by ROM represents a cost-effective, underutilized, and powerful diagnostic tool in the evaluation and management of FC, especially in patients who are refractory to empirical therapy with laxatives and dietary fiber. Its ability to objectively characterize colonic motility enables precise subtyping of constipation, guides tailored therapeutic interventions, and improves patient outcomes. Despite its established clinical value, ROM CTT studies remain underused in Asian countries due to gaps in awareness, lack of standardized protocols, and the absence of region-specific normative data. Addressing these challenges requires a multifaceted approach, including the adoption of simplified, validated protocols, the generation of multicentric normative data, the integration of ROM CTT assessment into clinical training and guidelines, and the harnessing of technological innovations such as AI-based radiograph interpretation. With strategic investment in education, research, and infrastructure, the ROM CTT study can be transformed from an underutilized diagnostic modality into a central pillar of constipation management, ultimately enhancing the quality of care for patients suffering from this chronic, debilitating disease.