Colorectal polyp size measurement comparing biopsy forceps with visual assessment during real-time colonoscopy: A prospective, multicenter, international study

Abstract

BACKGROUND

Colorectal polyp size is important for assigning appropriate surveillance intervals, but conventional visual assessment (VA) often results in size misclassification. The use of a biopsy forceps (BF) might improve polyp size assessment as suggested in current guidelines.

AIM

To compare measurement performance of BF-assisted size measurement with VA during real-time colonoscopy.

METHODS

A prospective, multicenter, international study was conducted at 5 tertiary hospitals. Patients aged ≥ 18 years scheduled for screening, surveillance, or diagnostic colonoscopy were included. Polyps were measured during colonoscopy with VA, BF, and a laser system (reference standard) and then removed and sent for histopathological assessment. The primary outcome was inter-method agreement of BF and VA compared to laser-based size measurement. Secondary outcomes included inter-method agreement between BF and VA and size misclassification. Furthermore, clinical implications were explored.

RESULTS

Among 110 patients, 276 polyps were detected, including 138 with successful reference laser-based measurements, of which 137 were analyzed. Moderate agreement was found for BF and VA compared to laser measurements (κ = 0.534 vs 0.514) with wide limits of agreement (± 3 mm), while almost perfect agreement (κ = 0.863) was observed between BF and VA. Both BF and VA underestimated polyp size by -0.16 mm and –0.11 mm, underestimating around 14%-50% of > 5 mm and ≥ 10 mm polyps and overestimating approximately 2%-11% of ≤ 5 mm and < 10 mm polyps. Around 2% of patients were assigned an incorrect surveillance interval using BF and VA, and when implementing a resect-and-discard strategy, 11% of ≤ 5 mm polyps would have undergone histopathology and 14% of > 5 mm polyps would have been discarded.

CONCLUSION

BF-assisted size measurement performs similarly to conventional VA, without improving precision or reducing size misclassification. Thus, BF can unlikely replace VA in routine colonoscopy, nor be recommended in clinical guidelines.

Key Words: Colonoscopy; Colorectal polyp; Polyp size; Biopsy forceps; Visual assessment; Laser system; Measurement agreement

Core Tip: Colorectal polyp size is visually assessed (VA) during colonoscopy, often causing misclassification and potentially leading to incorrect surveillance intervals. Biopsy forceps (BF)-assisted size measurement is recommended by European and American societies guidelines as it potentially reduces VA-related bias; however, its added value over VA is poorly studied. We prospectively evaluated measurement performance of BF and VA against reference laser-based measurements. Both techniques showed only moderate agreement with wide limits of agreement and resulted in a 2%-50% size misclassification. In contrast, BF and VA demonstrated almost perfect agreement with each other, suggesting limited added value of BF to VA.

INTRODUCTION

Recent updates of the European Society of Gastrointestinal Endoscopy (ESGE) and American Society of Gastrointestinal Endoscopy guidelines consider polyp size as an important factor for determining the optimal colonoscopy surveillance interval, since larger polyp size is associated with a higher risk of malignant transformation[1-3]. Polyp size estimation also has therapeutic consequences, as the threshold of ≤ 5 mm allows implementation of the resect-and-discard strategy[4]. Furthermore, estimated polyp size may guide the preferred endoscopic resection technique[4-6]. In current guidelines, polyp size is mainly determined through visual assessment (VA) performed by the endoscopist[2,3]. Unfortunately, size misclassification is common for VA due to terminal digit preference, image distortion due to the fish-eye lens of the endoscope, or fee-for-service financial incentives[7-11]. Size misclassification could lead to incorrect surveillance intervals, increasing the risk of post-colonoscopy colorectal cancer development or, in contrast, superfluous colonoscopies[12].

Biopsy forceps (BF) has been suggested by the ESGE and American Society of Gastrointestinal Endoscopy as a useful tool to assist in polyp sizing as it may avoid the above-mentioned biases related to VA[2,3]. However, few studies have examined the added benefit of BF-assisted size measurement over VA. Two studies found that BF-assisted size measurement improved polyp size measurement accuracy compared to VA (75.4% vs 69.3% and 71.3% vs 63.6%, respectively)[13,14]. However, a previous study showed that the mean error did not decrease when using BF for size measurement[15]. Moreover, Taghiakbari et al[11] concluded that BF-assisted size measurement did not show a significant reduction in interobserver variability and yielded mixed results regarding measurement accuracy improvement. Moreover, the use of BF leads to prolonged measurement duration[16]. Therefore, the aim of this study was to compare measurement performance of BF-assisted size measurement with VA during real-time colonoscopy compared to a reference standard.

MATERIALS AND METHODS

Study design and population

A multicenter, international study was conducted in 5 tertiary hospitals in the Netherlands, United States, and Israel between June 2023 and October 2025. Eligible patients were aged ≥ 18 years, and scheduled for screening, surveillance, or diagnostic colonoscopy. Polyps of all forms (flat, sessile, pedunculated) and ≤ 25 mm, as judged by the endoscopist, were considered eligible for inclusion. Up to three polyps per patient were included, to minimize extra time per patient and the potential influence of clustering. Patients were selected from inpatient and outpatient departments of the participating centers and were included in the study after informed consent had been signed. Exclusion criteria included a therapeutic colonoscopy; inflammatory bowel disease; an American Society of Anesthesiologists score of > 3; inadequately corrected anticoagulation disorder; inadequately managed periprocedural anticoagulation medication use; pregnancy; or inability to provide informed consent. Patients were also excluded during the colonoscopy when bowel preparation was found to be inadequate [Boston Bowel Preparation Scale (BBPS) of < 2 per segment]; when no polyps or only diminutive (≤ 5 mm) hyperplastic rectal polyps were identified; or when intraprocedural complications occurred. All eligible patients were included in the final analysis when they had at least 1 polyp that was measured with VA and BF and for which a size measurement with the reference standard of a laser-based measurement system was available.

Study procedures

During the colonoscopy, standard procedures for patient management and monitoring were used. In all procedures, conventional high-definition endoscopes (CF-HQ190 L, CF-HQ1100DL, EC38-i10, and EC-760Z) were used from Olympus (Tokyo, Japan), Pentax (Tokyo, Japan), or Fujifilm (Tokyo, Japan). A total of 8 endoscopists performed the colonoscopy procedures. During colonoscopy, once a polyp was identified, its size was measured with VA and then with BF in the open position. These size measurements were compared with in vivo laser-based size measurements which were taken immediately after the VA and BF-assisted size measurements (Figure 1). Laser-based size measurement was attempted at the endoscopist’s discretion, when measurement was considered feasible based on polyp location and size. The endoscopist performing the measurements remained blinded for the outcome of the laser-based size measurements to avoid a learning effect that could influence subsequent polyp size measurements. All polyps were photographically documented, excised and recovered for histopathological examination, except diminutive hyperplastic rectal polyps.

Figure 1 Workflow overview of colorectal polyp size measurement via visual assessment, biopsy forceps, and the laser-based measurement system. A: Measurement of a sessile (0-Is) serrated polyp located in the ascending colon; B: Measurement of a 0-Is adenoma located in the rectum. The laser-based measurement images on the right show the two points indicated by the user and the respective 3D Euclidean distance.

Laser-based polyp size measurement

The laser-based measurement system (AccuMeasure, VTM technologies Ltd., Haifa, Israel) received De Novo United States Food and Drug Administration authorization (DEN210032; July 26, 2022) and its clinical application has been discussed in prior studies[17-19]. In brief, the laser-based measurement system consists of a through-the-scope laser-emitting probe, accompanied by proprietary measuring software. The through-the-scope probe projects a laser line across the polyp, enabling size measurement. The software conducts the measurement based on two points on the image along the laser line that are indicated by the user at either side of the polyp, and the respective 3D Euclidean distance is displayed. For this study, an independent reviewer selected the laser endpoints at either side of the polyp. Afterwards, the laser endpoint selection was reviewed by the research coordinator (Gerritsen D) and a participating endoscopist (Rijckborst V), while blinding of the endoscopist was maintained by ensuring that the size measurements were not displayed alongside the chosen endpoints on the images. Each laser-based polyp measurement was repeated five times under blind conditions to capture intra-observer variation in selecting endpoints, and the mean laser-based polyp measurement was used as reference measurement. All participating endoscopists were required to perform 4 practice cases with the laser system prior to study enrollment to become familiar with the system.

Data collection

Colonoscopy data included procedure date and indication, endoscopist, and BBPS. Patient data consisted of age, sex, personal/family history of polyps or colorectal cancer, and American Society of Anesthesiologists classification. Polyp data included polyp size according to the different measurement techniques (VA, BF, and laser system), polypectomy technique, colonic segment, polyp morphology according to the Paris classification, and measurement duration.

Outcome measures

The primary outcome was the inter-method agreement in determining polyp size using BF and VA compared with the reference laser-based size measurements for polyps categorized into ≤ 5 mm, 6-9 mm, and ≥ 10 mm. Secondary outcomes included inter-method agreement between VA and BF and size misclassification. Clinical implications and adverse events (AEs) and serious AEs up to 30 days post-colonoscopy were also explored.

Statistical analysis

Categorical and continuous data were presented as mean ± SD, median [interquartile range (IQR)], or frequencies, where appropriate. The Cohen’s Kappa coefficient (κ) was calculated to determine the inter-method agreement. This coefficient was defined as 0 (poor), 0 to 0.20 (slight), 0.21 to 0.4 (fair), 0.41 to 0.60 (moderate), 0.61 to 0.8 (substantial), and ≥ 0.81 (almost perfect)[20]. Bland-Altman plots were used to further evaluate agreement but also size misclassification and precision between two techniques by means of the mean difference (MD), limits of agreement (LoA), and the presence of size dependent measurement error[21]. Moreover, systematic differences between the measurement techniques were assessed with linear mixed regression models with measurement techniques as fixed effects (independent variable) and endoscopists and polyps as random effects. Subgroup analyses, based on different polyp subtypes and participating endoscopists, were performed. All statistical analyses were done with a significance level of 5% and were performed with SPSS (version 28.0.1). The statistical methods of this study were reviewed by a dedicated statistician from the statistical analysis department of Erasmus University Medical Center.

Sample size

Colorectal polyps were taken as unit of analysis for this study, meaning that as many patients were included as needed to achieve the required number of polyp size measurements. This study was powered to detect substantial inter-method agreement (κ = 0.7) for the following categories: ≤ 5 mm, 6-9 mm, ≥ 10 mm. A prevalence of 60%, 30%, and 10% was assumed for polyps of ≤ 5 mm, 6-9 mm, and ≥ 10 mm, respectively[22]. Using the KappaSize package in R with a two-sided alpha of 0.05, a power of 0.80, and a 10% drop-out rate, 138 polyp measurements were required[23].

RESULTS

Patient and polyp characteristics

A total of 188 patients were checked for eligibility, and 187 eligible patients were recruited (Figure 2). Of these patients, 60 (32.1%) were excluded because no polyps were identified, 16 (8.6%) because of poor bowel preparation, and 1 (0.5%) because of an intraprocedural complication. The remaining 110 patients were included in the analysis with 56.4% being male and a median age of 68 years (IQR = 18.0) (Table 1). A total of 276 polyps were detected during screening, surveillance, and diagnostic colonoscopies. Among these, 199 polyps were attempted to be measured with the laser system, which yielded 138 successful measurements, corresponding to a technical success rate of 69.3%. Unsuccessful laser-based measurement was mainly attributed to technical difficulties such as failed probe tip recognition and software malfunctioning, which occurred in 50.8% of the failed measurements (Supplementary Table 1).

Table 1 Patients’ demographic and baseline characteristics, n (%).

Parameter	Value
No. of patients	110
Age (years), median (IQR)	68 (18.0)
Sex
Male	62 (56.4)
Female	48 (43.6)
Personal history adenoma	56 (50.9)
Personal history CRC	8 (7.3)
Family history CRC	20 (18.2)
BBPS score, median (IQR)	7 (3.0)
Colonoscopy indication
Screening	47 (42.7)
Surveillance	34 (30.9)
Diagnostic	29 (26.4)

BBPS: Boston Bowel Preparation Scale; CRC: Colorectal cancer; IQR: Interquartile range.

Figure 2 Flowchart of patient and polyp selection. ASA: American Society of Anesthesiologists score; BBPS: Boston Bowel Preparation Scale.

All 138 polyps that were successfully measured with the laser-based measurement system, were also measured using VA and BF. One polyp was excluded during analysis as it was measured in an excluded patient with a BBPS of 5, leaving 137 polyps which were measured. From these, 91 polyps (66.4%) were adenomas and 35 (25.6%) were serrated polyps, according to histopathological examination (Table 2). The mean polyp size measured with BF and VA was 4.00 ± 2.00 mm, while this was 4.50 ± 2.16 mm for the laser system. According to the laser-based measurements, 115 polyps were ≤ 5 mm, 18 were 6-9 mm, and 4 were ≥ 10 mm. VA-related size measurement took approximately 10 to 15 seconds, while the median duration for measuring with BF was 32 seconds (IQR = 29.3) and with the laser system 88 seconds (IQR = 81.0), respectively. Patient and polyp characteristics in each participating hospital are presented in Supplementary Tables 2 and 3.

Table 2 Polyp characteristics, n (%).

Parameter	Value
No. of polyps	137
Anatomical location
Cecum	14 (10.2)
Ascending	32 (23.4)
Transverse	36 (26.3)
Descending	30 (21.9)
Sigmoid	20 (14.6)
Rectum	5 (3.6)
Polyp size categories1
≤ 5 mm	115 (83.9)
6-9 mm	18 (13.1)
≥ 10 mm	4 (3.0)
Polyp type
Adenoma	91 (66.4)
Serrated	35 (25.6)
Other	8 (5.8)
Missing	3 (2.2)
Paris classification
0-Ip	8 (5.8)
0-Is	75 (54.7)
0-IIa	52 (38.0)
Missing	2 (1.5)
Resection method
Cold snare	86 (62.8)
Hot snare	8 (5.8)
EMR	1 (0.7)
Missing2	42 (30.7)

¹Number of polyps per size category based on the reference laser-based size measurements.

²In 3 of 5 participating hospitals, the resection method was not routinely recorded as part of the standardized data collection procedure, resulting in missing information for 42 polyps.

EMR: Endoscopic mucosal resection.

Inter-method agreement and precision

Moderate agreement (κ = 0.534, 95%CI: 0.375-0.693) was observed between BF and the reference size measurements by the laser system, which was similar compared to the moderate agreement (κ = 0.514, 95%CI: 0.357-0.671) between VA and the laser system. There was almost perfect agreement (κ = 0.863, 95%CI: 0.765-0.961), when comparing BF and VA directly.

Based on subgroup analyses, the agreement between BF and the laser system was lowest for pedunculated (0-Ip) polyps (κ = 0.333, 95%CI: -0.055 to 0.721) while this was lowest for flat elevated (0-IIa) polyps (κ = 0.427, 95%CI: 0.182-0.672) between VA and the laser system. For the participating endoscopists, agreement between BF and the laser system ranged from κ = 0.368 (95%CI: -0.104 to 0.840) to κ = 0.654 (95%CI: 0.333-0.975), and from κ = 0.368 (95%CI: -0.104 to 0.840) to κ = 0.726 (95%CI: 0.358-1.094) between VA and the laser system, respectively. The agreement between BF and VA was perfect (κ = 1.000) for 5 out of 8 endoscopists.

As seen in the Bland-Altman plots (Figure 3), BF and VA agreed moderate to poor and were imprecise compared to the reference size measurements as both techniques differed up to 3 mm for size assessment of an individual polyp (LoA: -2.72 to 2.39 mm and -3.32 mm to 3.10 mm, respectively). There was a LoA of -1.36 mm to 1.26 mm between BF and VA.

Figure 3 Bland-Altman plots. A: Size differences (in millimeters) between biopsy forceps and the laser-based measurement system; B: Size differences (in millimeters) between visual assessment and the laser-based measurement system; C: Size differences (in millimeters) between biopsy forceps and visual assessment. Each point in the plots represents one polyp measurement and shows the difference in size (in millimeters) for all 137 polyps. The blue line represents the mean difference in millimeters between two measurement techniques. The red lines indicate the upper and lower limits of agreement, which is the range containing the most size differences between two measurement techniques. BF: Biopsy forceps; VA: Visual assessment.

Size misclassification

For polyps across all size categories, BF-assisted size measurement resulted in a statistically non-significant mean underestimation with a MD of -0.16 mm (95%CI: -0.38 to 0.06) compared to the reference size measurements, which was similar to the mean underestimation found for VA with a MD of -0.11 mm (95%CI: -0.39 to 0.17) as seen in the Bland-Altman plots (Figure 3). Only VA compared to BF showed statistically significant size dependent measurement error (P = 0.012 vs P = 0.118, respectively). Endoscopists tended to underestimate polyp size for ≤ 5 mm polyps while overestimating polyp size for > 5 mm polyps onwards with approximately 0.46 mm when relying solely on VA, with larger polyps showing greater overestimation.

Overall, 13.6% of > 5 mm polyps were underestimated as ≤ 5 mm with both BF and VA compared to the laser system (Table 3). Conversely, 11.3% of ≤ 5 mm polyps were overestimated as > 5 mm with both BF and VA. A total of 50.0% of ≥ 10 mm polyps were underestimated as < 10 mm with both BF and VA. Contrarily, 2.3% of < 10 mm polyps were overestimated as ≥ 10 mm with BF vs 3.0% with VA. A linear mixed-effects model demonstrated that polyp-specific factors attributed approximately 85% to the size differences found between the measurement techniques. This is supported by the previously mentioned subgroup analysis, in which BF and VA showed the lowest agreement with the laser system for 0-Ip and 0-IIa polyps.

Table 3 Polyp size misclassification using biopsy forceps-assisted size measurement and visual assessment compared to the reference laser-based size measurements.

Polyp size misclassifications, n/N (%)1	BF	VA
> 5 mm2 as ≤ 5 mm	3/22 (13.6)	3/22 (13.6)
≤ 5 mm as > 5 mm	13/115 (11.3)	13/115 (11.3)
≥ 10 mm as < 10 mm3	2/4 (50.0)	2/4 (50.0)
< 10 mm as ≥ 10 mm	3/133 (2.3)	4/133 (3.0)

¹n = number of polyps misclassified by biopsy forceps and/or visual assessment and N = number of polyps in the respective size category based on the reference laser-based size measurements.

²> 5 mm category is the 6-9 mm category combined with the ≥ 10 mm category.

³< 10 mm category is the ≤ 5 mm category combined with the 6-9 mm category.

BF: Biopsy forceps; VA: Visual assessment.

Clinical implications

Around 2% of patients were assigned an incorrect surveillance interval due to overestimation at the 10 mm threshold with BF and VA based on the ESGE guidelines compared to the reference size measurements with the laser system[2]. Based on both BF and VA, one patient was assigned a surveillance interval of 3 years as 2 polyps were encountered, of which 1 polyp had been assessed as a 10 mm sessile (0-Is) adenoma located in the ascending colon. Based on laser-based measurement (9 mm), this patient should have been assigned a surveillance interval of 10 years. Another patient was assigned a surveillance interval of 5 years based on a VA measurement of 10 mm for one 0-IIa hyperplastic polyp located in the descending colon. Based on the BF-assisted size measurement and the laser-based measurement (± 8 mm), this patient should also have been assigned a surveillance interval of 10 years.

If a resect-and-discard strategy had been implemented using both BF and VA, 11.3% of ≤ 5 mm polyps as based on laser-based measurement would have been sent for histopathological examination. Contrarily, when using both BF and VA 13.6% of > 5 mm polyps as based on laser-based measurement would incorrectly have been discarded.

Safety

During the study, 6 AEs (5.5%) and 1 serious AE (0.9%) occurred. One AE of post-polypectomy fever and pain within 24 hours was managed conservatively and had a probable relationship to the colonoscopy. The other serious AEs were not related to the colonoscopy and included congestive heart failure exacerbation, COVID-19 infection, diagnosis of benign prostatic hyperplasia and erectile dysfunction, presence of renal cysts, onset of diarrhea related to colitis, and post-polypectomy bleeding not requiring therapy.

DISCUSSION

This multicenter, international study demonstrated that BF performed largely similar to VA and does not provide improved precision nor a reduction in size misclassification. Only moderate agreement between BF and the reference laser system was found as well as between VA and the laser system, with no difference between BF and VA. Both BF and VA had wide LoA’s and resulted in a mean underestimation of polyp size with clinical implications around the 5 and 10 mm thresholds, misclassifying around 2%-50% of polyps.

Polyp size is still primarily estimated visually, a method that is known to be imprecise and prone to misclassification[7-11]. BF has been proposed as a useful tool to combat VA-related bias and suggested to give more precise polyp size measurements[2,3]. Our study confirmed that VA is imprecise compared to the reference laser-based measurements, but the use of BF did not provide more precise size measurements over VA. In line with our results, a previous ex vivo animal study also demonstrated that both BF and VA were considerably less precise than the laser system, showing large absolute differences from the reference caliper-based size measurements (3.64 ± 2.37 mm and 4.68 ± 2.89 mm, respectively) compared with the markedly smaller difference observed with the laser system (0.55 ± 0.31 mm)[17]. A plausible explanation for the lack of improved precision with BF-assisted measurement is a combination of image distortion produced by the endoscope’s wide-angle, fish-eye lens and inconsistent viewing distances[10]. Additionally, polyp morphology might also influence the precision of the BF-assisted size measurement as the agreement between BF and the laser system was lowest for 0-Ip polyps, suggesting that measurement with a BF might not be useful for all polyps.

An objective and precise reference standard for polyp sizing is required for the evaluation of measurement techniques. We therefore used a laser-based measurement system as reference standard, which was validated against caliper and microscopy measurements and previously found to result in objective and accurate polyp sizing with minimal bias (-0.10 mm, 95%CI: -0.30 to 0.10; P = 0.328) and a 95.1% accuracy (39/41, 95%CI: 82.2-99.2) with no AEs[17-19]. However, overall performance and usability of this system was found to be sub-optimal in our study. Laser-based measurements were not performed at the discretion of the endoscopist for 77 polyps. Reasons included unfavorable polyp location or polyp size larger than 25 mm, making a continuous laser line projection not possible. Moreover, among attempted measurements, successful laser-based measurement was obtained in only 69.3%, indicating moderate technical success. Failures occurred due to technical difficulties including problems coupling the probe to the software, software malfunctioning, and anatomical interference such as peristalsis. This raises the possibility of selection bias, as the assessed polyps may have differed systematically in size, morphology and type from those that were not assessed, potentially resulting in a set of polyps that are not fully representative of the polyps encountered during routine colonoscopy. However, these exclusions reflect the usability of the laser system rather than a deliberate selection of polyps. Lastly, the median measurement duration for the laser system was 88 seconds. Together, these findings reflect the limited usability of this system during routine colonoscopies, which is in line with a recent pilot study that also showed a modest technical success rate of 40.9% and a mean measurement duration of 95 seconds[19]. While this system is not yet practical for routine colonoscopy, the system’s objective measurements and high accuracy could make it a valuable reference standard for future polyp sizing studies.

Alternative measurement systems may therefore be more suitable for polyp size measurement during routine colonoscopies, including a virtual scale endoscope (VSE). VSE could potentially also be hindered by anatomical interference issues, but the software appears to be more stable in clinical practice leading to a higher measurement success rate[24-27]. Moreover, VSE showed a lower reported measurement duration of approximately 40 seconds[27-29]. Artificial intelligence might provide another alternative approach to polyp size measurement, as some previous studies suggested that artificial intelligence provides objective and fast measurements with no need for using a separate device, combining the advantages of both the laser system and VSE[30-32]. However, current evidence remains so far preliminary with limited validation against precise reference standards.

Djinbachian et al[14] found that approximately 10% of diminutive polyps were overestimated as > 5 mm with BF and 15% of polyps with VA. We found similar results with about 11% of diminutive polyps being overestimated as > 5 mm with both VA and BF-assisted size measurement leading to unnecessary histopathological assessments. In our study, around 2% of patients were assigned a surveillance interval that was too short due to overestimation at the 10 mm threshold with BF and VA. In 2024, 57825 patients underwent a screening colonoscopy after a positive fecal immunochemical test in the Netherlands with an anticipated detection rate of 2.39 polyps per colonoscopy[33,34]. This detection rate is based on a European study including 25 academic hospitals, 14 hospitals, 8 private institutions, 3 group practices, and 1 other with a total of 3356 diagnostic and screening colonoscopies[34]. When extrapolating these data, approximately 1157 patients would have undergone a superfluous colonoscopy after 3 years and approximately 15202 polyps are expected to be sent for unnecessary histopathological examination due to VA or BF-assisted size assessment imposing a substantial burden on the Dutch healthcare resource utilization and associated costs.

This study has several strengths, including its multicenter, international design, which ensures that the findings reflect diverse patient populations, endoscopy systems, and clinical practices. Additionally, blinding endoscopists to the laser-based measurement outcomes prevented endoscopists from discerning any tendencies to over- or underestimate polyp size, thereby ensuring that their VA and BF-assisted size measurements remained unbiased. Moreover, we are the first to objectively demonstrate that VA leads to an underestimation of ≤ 5 mm polyps and overestimation of > 5 mm polyps, with the degree of overestimation increasing at larger sizes influencing surveillance interval assignment. Lastly, the prospective inclusion of different sized polyps with distinct morphology provided real-world insights into the clinical limitations of BF as a sizing tool.

It is however also important to note some limitations such as the limited number of ≥ 10 mm polyps that were included. This complicates drawing firm conclusions on the clinical impact of BF-assisted size measurements for surveillance interval assignment. Future studies should assess BF-assisted measurement precision in more detail for these larger polyps (≥ 10 mm). Another limitation is the potential lack of independency between BF and VA-related size measurements as endoscopists tended to take over their initial VA determined size during BF-assisted size measurement. This limits the interpretation of the agreement between BF and VA and should be considered when concluding that the two techniques have similar performance. Ideally, size measurements with BF and VA should be obtained independently, which is however not feasible in clinical practice. The next best approach would be to randomize the order of BF and VA-related size measurements, as this could reduce potential order effects and provide a more robust assessment of agreement between the two techniques. However, this is also less feasible because the endoscopist immediately makes a visual estimate of polyp size upon inspection, influencing the subsequent measurements regardless of measurement order. Due to the moderate technical success rate of laser-based measurement, it took longer than expected to reach the required number of polyps measured with all three techniques (BF, VA, and laser system). Laser probe refinement and integration of the probe into endoscopes might however well reduce the technical difficulties found in this study. Lastly, the study was powered to detect substantial inter-method agreement (κ = 0.7) for the categories: ≤ 5 mm, 6-9 mm, ≥ 10 mm. However, the observed kappa values were approximately 0.5 between BF and the laser system and between VA and the laser system, corresponding to moderate agreement. Therefore, the study may not have achieved the level of agreement as anticipated in the original sample size calculation. The findings should therefore be interpreted as evidence of comparable moderate agreement between BF and VA rather than formal equivalence.

CONCLUSION

Our study shows that BF-assisted size measurement performs similarly to conventional VA, without improving precision or reducing size misclassification, thus offering no meaningful improvement in measurement performance. Based on our findings, the use of BF for colorectal polyp size measurement could not replace VA in routine colonoscopy, nor should it be recommended in future revisions of clinical guidelines. However, more research needs to be conducted including larger sample sizes and more ≥ 10 mm polyps.

ACKNOWLEDGEMENTS

The authors would like to thank VTM Technologies for providing the laser-based measurement system.