Determinants of high sessile serrated lesion detection: Role of faecal occult blood test and colonoscopy quality indicators

Abstract

BACKGROUND

Sessile serrated lesions (SSLs) are premalignant polyps implicated in up to 30% of colorectal cancers. Australia reports high SSL detection rates (SSL-DRs), yet with marked variability (3.1%-24%). This substantial variation raises concerns about missed lesions and post-colonoscopy colorectal cancer. This study investigates determinants associated with SSL-DR variation in regional Australia.

AIM

To study how patient, clinical, and colonoscopy factors are associated with SSL detection in a regional Australian practice. We aimed to contribute high-detection data to the literature by analyzing the association of SSL detection with various determinants.

METHODS

This retrospective, cross-sectional analysis examined 1450 colonoscopies performed at Port Macquarie Gastroenterology during 2023. Sigmoidoscopies and repeat procedures were excluded. Multivariate logistic regression analyzed associations between SSL detection and patient demographics, clinical indications, procedural factors, and comorbidities.

RESULTS

The overall SSL-DR was 30.7%. Multivariate analysis identified several independent predictors: Clinical indication, bowel preparation quality, inflammatory bowel disease status, and serrated polyposis syndrome. The faecal occult blood test positive (FOBT) (+) cohort showed the highest predicted SSL detection probability (39.8%), while clinical symptoms showed the lowest (22.3%). After adjustment, SSL detection odds were 2.3 times greater among FOBT (+) patients than those with clinical symptoms (adjusted odds ratio = 2.30, 95% confidence interval: 1.20-4.40, P = 0.004).

CONCLUSION

SSL-DR as a quality indicator requires contextualization regarding clinical indications, bowel preparation quality, and comorbidities. There was a significantly higher prevalence of SSLs in FOBT (+) patients. Despite comprehensive adjustment, this study cannot fully explain the wide SSL-DR variation in Australia, highlighting the need for standardized detection protocols and further research to ensure optimal cancer prevention outcomes.

Key Words: Sessile serrated lesion; Adenoma detection rate; Faecal occult blood test; Polyp detection rate; Dysplasia; Colonoscopy; Prevalence

Core Tip: This study reports an exceptionally high sessile serrated lesion detection rate of 30.7% in regional Australia, with faecal occult blood test positive-positive patients showing the highest rate (42%). Clinical indication, bowel preparation quality, inflammatory bowel disease status, and serrated polyposis syndrome were identified as independent predictors. The marked variability in sessile serrated lesion detection rate across Australia (3.1%-24%) highlights the need for standardized detection protocols and context-specific quality indicators to optimize colorectal cancer prevention.

INTRODUCTION

Background and significance of sessile serrated lesions

Colorectal cancer (CRC) represents the third most frequently diagnosed non-cutaneous malignancy globally and the second leading cause of cancer mortality[1-4]. While the traditional “adenoma-carcinoma sequence” explains the majority of cases, emerging evidence indicates that up to 30% of sporadic CRC cases arise via the “serrated neoplasia pathway” from serrated lesions[1,5-7].

Recent World Health Organization classification updates replaced the term sessile serrated adenoma/polyp with sessile serrated lesion (SSL), simplifying diagnostic criteria to require only one unequivocal aberrant crypt[8,9]. This clarification has improved inter-observer agreement among pathologists and increased SSL diagnosis rates[10-13].

SSLs have established malignant potential, with dysplastic SSLs (dSSLs) representing an intermediate step toward CRC[14]. Though dSSLs comprise only 2%-5% of all SSLs[1,15-17], this likely reflects rapid progression to carcinoma rather than rare dysplastic transformation[18]. Once dysplasia develops, progression to invasive carcinoma accelerates significantly[14,19].

Due to challenges in endoscopic differentiation, current guidelines recommend removing all serrated lesions except diminutive distal hyperplastic polyps[20,21]. CRCs originating from serrated lesions are disproportionately represented among post-colonoscopy CRCs (PCCRCs), attributed to rapid malignant transformation, detection difficulties, and incomplete resection[22].

International studies show marked variation in SSL detection rates (SSL-DRs)[5,23,24]. Meta-analyses reveal significant geographic disparities: Western countries demonstrate rates of 4.3% [95% confidence interval (CI):1.2%-6.0%] vs 0.4% (95%CI: 0.2%-0.9%) in Eastern countries[23]. Notably, Australia reports significantly higher SSL-DRs at 10.5% (95%CI: 2.8-18.2%) compared to the United States at 5.1% (P = 0.03) - providing important context for the present study[24,25].

Significance of detection rates

Crockett and Nagtegaal[5] reported international SSL-DRs generally between 2% to 8%, with high-detection centers exceeding 20%. They suggested that rates achieved by high-detectors may better reflect true SSL prevalence, implying that significant variations in SSL-DR indicate many SSLs go undetected[5,26].

Recent studies confirm the clinical significance of SSL-DRs, with higher detection rates protecting against PCCRC[27]. Anderson et al[27] demonstrated a 71% PCCRC reduction in the highest SSL-DR quintile (> 6%; hazard ratio = 0.29; 95%CI: 0.16-0.50). European research shows similar protective effects independent of adenoma detection rates (ADRs)[26,28,29].

Australian data remains limited without a comprehensive national colonoscopy registry outside the National Bowel Cancer Screening Program[30]. Recent Australian studies report SSL-DRs ranging from 3.1% to 24% - an almost eight-fold variation (Table 1). Higher SSL-DRs correlate with quality indicators including adequate bowel preparation, high caecal intubation rates, longer withdrawal times, and higher ADRs[2,10,11,21,24], though all cited studies reported acceptable colonoscopy quality metrics[1,2,10,11,17,20,21,25].

Table 1 Recent Australian studies reporting the sessile serrated lesion detection and similar metrics.

Ref.	Study focus	Number of colonoscopies	Colonoscopist		SSL-DR
			Specialty	Number	Rate	Value
Zhang et al[1], 2023	SSLDRs prevalence	21903	NR	NR	SSL-DR	24.0%
Haga et al[2], 2022	Rural QI performance	1674	GP	3	CSSDR	14.2%
					PSDR	16.0%
Watson et al[10], 2023	Rural QI performance	3497	GS	24	CSSDR	5.4%
			GS Reg	12
Wong et al[11], 2020	Withdrawal times	1579	GS	NR	SSL-DR	5.4%
Zorron Cheng Tao Pu et al[21], 2019	Specialty and time of day	2657	GE	9	SSL-DR	7.1%
			Surgeons	6		4.9%
Wong et al[36], 2017	Age in years, < 50 vs ≥ 50	2013	NR	NR	SSL-DR	3.1%
Bettington et al[17], 2017	SSL prevalence	707	GE	1	SSL-DR	19.8%
Kumbhari et al[25], 2013	Caucasian vs Asian	1000	GE	1	SSL-DR	5.3%

Rates are reported for all indications. For simplicity, only the lead author is listed in the “Study” column. In some Australian studies, the sessile serrated lesion (SSL) detection rate was not always directly reported, and a review of the number of colonoscopies and patients with SSLs was required. Some studies reported alternative metrics, such as the clinically significant serrated polyp detection rate and proximal serrated polyp detection rate, and the SSL detection rate could not be determined from supplementary tables. SSLDs: Sessile serrated lesion detection rate; NR: Not reported; QI: Quality indicator; GP: General practitioner; GE: Gastroenterologists; GS: General surgeons; GS Reg: General surgical registrars; SSL-DR: Sessile serrated lesion detection rate; CSSDR: Clinically significant serrated polyp detection rate; PSDR: Proximal serrated polyp detection rate.

MATERIALS AND METHODS

Study design

A retrospective, single-centre, cross-sectional study evaluated SSL-DRs and associated factors among patients undergoing colonoscopy between 1 January 2023 and 31 December 2023.

Setting

The study was conducted at Port Macquarie Gastroenterology (PMG), which serves the local community and greater Mid North Coast region of New South Wales, Australia. All procedures were performed at Port Macquarie Private Hospital (PMPH), the only accredited private facility for colonoscopy in the area. Two consultant gastroenterologists with current Gastroenterological Society of Australia recertification in Adult Colonoscopy performed all colonoscopies during 2023.

Participants

The study included all patients who underwent colonoscopy with PMG at PMPH during the study period. The exclusion criteria were: (1) Patients who underwent sigmoidoscopy only; and (2) For patients with multiple colonoscopies in 2023, only the first procedure was included in the analysis to avoid bias from repeat procedures.

Clinical practices

Patients received split-dose polyethylene glycol solution (MoviPrep^®, Norgine) for bowel preparation, with sodium picosulfate (PicoSalax^®, Ferring) used for polyethylene glycol solution-intolerant patients. Procedures were performed using Olympus EVIS EXERA III (CV-190) processors with CF-H190 or CF-HQ190 colonoscopes. Endoscopist 1 routinely used the EndoCuff^® device (Olympus) for enhanced mucosal visualization, while endoscopist 2 did not. Douglas Hanley Moir Pathology conducted all histopathological assessments, with specialist gastrointestinal histopathologists verifying all dSSL diagnoses during dedicated pathology meetings. In accordance with the current WHO criteria a single, unequivocally distorted crypt was the minimum criterion used for diagnosing an SSL[8].

Data collection

Data was manually extracted from PMG practice software (Genie version 9.2.2., Magic Carpet Software Solutions). The schedule for each day in 2023 was reviewed, and each patient listed as having undergone a colonoscopy had relevant data collected from their profile, endoscopy report and pathology report.

Variables and definitions

Patient demographics were obtained from practice software, while procedural information (indication, endoscopist, Boston Bowel Preparation Score, polypectomy number, and intubation depth) came from endoscopy reports. Histopathological reports provided polypectomy details including polyp type and location. Inflammatory bowel disease (IBD) and serrated polyposis syndrome (SPS) were presumed absent unless documented otherwise. Table 2 outlines the methodology for recording indications, BBPS and SPS classification transformations, and definitions of polypectomy-specific quality indicators.

Table 2 Special definitions and data transformations.

Characteristic	Terms	Explanation
Variables	Indication	For the purpose of this study, each colonoscopy was assigned only a single indication using a hierarchical coding system, with the following priority order: (1) Clinical symptoms; (2) FOBT (+); (3) Surveillance (previous patient); (4) Surveillance (new patient); and (5) Screening
	Bowel preparation status	Boston Bowel Preparation Scores were collated into three broad groups: Inadequate (BBPS ≤ 5), adequate (BBPS 6 or 7), good (BBPS 8 or 9)
	Serrated polyposis syndrome status	This variable amalgates the distinction between those with SPS diagnosed in a previous colonscopy and those with SPS diagnosed from the present colonoscopy. It represents whether SPS classified as present or absent
Polypectomy quality indicators	Polypectomy rate	The proportion of colonoscopies during which at least one polypectomy was performed
	ADR	The proportion of colonoscopies during which at least one conventional adenomatous polyp, (tubular adenomas, tubulovillous adenomas, or villous adenomas) was detected. Excludes malignancies
	ASLDR	The proportion of colonoscopies during which at least one serrated lesion was detected
	SPDR	The proportion of colonoscopies during which at least one SSL/dSSL or TSA is detected. Excludes HPs
	PSDR SDR	The propotion of colonoscopies during which at least one of any serrated lesion (HP, SSL, dSSL, or TSA) is detected proximal to the border between the descending and sigmoid colon
	SSL-DR	The proportion of colonoscopies during which at least one SSL, dSSL is detected

FOBT (+): Faecal occult blood test positive; BBPS: Boston bowel preparation scale; SPS: Serrated polyposis syndrome; SSL: Sessile serrated lesion; dSSL: Dysplastic sessile serrated lesion; ADR: Adenoma detection rate; ASLDR: Any serrated lesion detection rate; SPDR: Serrated polyp detection rate; PSDR: Proximal serrated detection rate; TSA: Traditional serrated adenoma; SSL-DR: Sessile serrated lesion detection rate; SDR: Serrated detection rate; HP: Hyperplastic polyp.

Statistical analysis

Data was collated and analyzed using Microsoft Excel (Microsoft Corporation, 2024) and RStudio (Posit Software, 2024). Descriptive statistics summarized patient demographics, clinical features, and quality indicators. Continuous variables were presented as means with standard deviations, and medians with ranges. Categorical variables were summarized as counts and percentages. We performed multivariable logistic regression to examine conditional associations between SSL detection and other variables. Specifically, we modelled SSL detection with respect to patient age at colonoscopy, patient sex, indication for colonoscopy, endoscopist, bowel preparation quality, IBD status, and sessile serrated polyposis status. Model assumptions were verified using quantile residual plots. Estimated marginal means were calculated to provide predicted probabilities of SSL detection for each factor and odds ratios from pairwise contrasts with Tukey’s method for all categorical data. While the conventional alpha of 0.05 was used, as an exploratory study, greater emphasis was placed on trends and effect sizes. Similarly, a formal power analysis was not performed.

Ethics

Ethical approval was obtained from the University of New South Wales Human Research Ethics Advisory Panel D, No. IRECS0829. The study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki.

RESULTS

Participants

Between 1 January 2023 and 31 December 2023, the two gastroenterologists at PMG performed a total of 1462 colonoscopies at the PMPH. Both Gastroenterologist had over 10 years’ experience with lifetime procedural volume of over 5000 colonoscopies each. Of these, 12 colonoscopies occurred in patients who had a previous colonoscopy with PMG during 2023, and data from these colonoscopies was removed. The remaining 1450 colonoscopies represent the only/first colonoscopy of each patient in 2023 and formed the study sample presented subsequently.

Study sample characteristics

In the study sample, females accounted for 59.3% of patients, and the median patient age at colonoscopy was 69.2 years, ranging from 16.3 years to 93.5 years. The most common indication was surveillance of a previous patient (54.6%), followed by clinical symptoms (28.9%). A diagnosis of IBD was present in 3.7% of patients, and there was a new or existing diagnosis of SPS in 7.9% of patients. Of note, there were 10 new diagnoses of SPS, or 0.7% of the colonoscopy sample. Approximately 65.0% of patients achieved good bowel preparation with a BBPS of 8% or 9%, 30.3% achieved adequate bowel preparation with a BBPS of 6% or 7%, and the remaining 4.8% had inadequate bowel preparation with a BBPS of 5% or less (including those not scored). The caecal intubation rate was high, with the terminal ilium intubated in 99.0% of colonoscopies. Endoscopist 1 completed 86.5% of colonoscopies, and the remainder were completed by endoscopist 2. The SSL-DR was 31.6% for Endoscopist 1, and 24.5% for endoscopist 2 (Table 3).

Table 3 Patient demographics and colonoscopy characteristics, n (%).

Characteristic	SSL detections		Overall (n = 1450)	Respective SSL-DRs, %
	None (n = 1005)	At least one (n = 445)
Age at colonoscopy
mean ± SD	66.6 ± 13.2	66.7 ± 13.3	66.6 ± 13.2	N/A
Median (minimum-maximum)	68.8 (17.0-93.5)	69.8 (16.3-92.2)	69.2 (16.3-93.5)	N/A
Patient sex
Male	408 (40.6)	182 (40.9)	590 (40.7)	30.8
Female	597 (59.4)	263 (59.1)	860 (59.3)	30.6
Indication
Clinical symptoms	317 (31.5)	102 (22.9)	419 (28.9)	24.3
FOBT (+)	58 (5.8)	42 (9.4)	100 (6.9)	42.0
Surveillance (previous patient)	541 (53.8)	251 (56.4)	792 (54.6)	31.7
Surveillance (new patient)	45 (4.5)	29 (6.5)	74 (5.1)	39.2
Screening	44 (4.4)	21 (4.7)	65 (4.5)	32.3
Bowel preparation status
Inadequate (BBPS ≤ 5)	58 (5.8)	11 (2.5)	69 (4.8)	15.9
Adequate (BBPS 6 or 7)	311 (30.9)	128 (28.8)	439 (30.3)	29.2
Good (BBPS 8 or 9)	636 (63.3)	306 (68.8)	942 (65.0)	32.5
Serrated polyposis syndrome diagnosis
Absent	959 (95.4)	377 (84.7)	1336 (92.1)	28.2
Prior	46 (4.6)	58 (13.0)	104 (7.2)	55.8
New	0 (0)	10 (2.2)	10 (0.7)	100.0
Inflammatory bowel disease
Absent	959 (95.4)	437 (98.2)	1396 (96.3)	31.3
Present	46 (4.6)	8 (1.8)	54 (3.7)	14.8
Endoscopist
1	857 (85.3)	397 (89.2)	1254 (86.5)	31.6
2	148 (14.7)	48 (10.8)	196 (13.5)	24.5
Intubation depth
Terminal ilium	992 (98.7)	443 (99.6)	1435 (99.0)	30.9
Caecum	3 (0.3)	2 (0.4)	5 (0.3)	40.0
Not to caecum	7 (0.7)	0 (0)	7 (0.5)	0.0
No comment	3 (0.3)	0 (0)	3 (0.2)	0.0
Colonoscopy occurrences in 2023
Sole colonoscopy	996 (99.1)	442 (99.3)	1438 (99.2)	30.7
First colonoscopy	9 (0.9)	3 (0.7)	12 (0.8)	25.0

FOBT (+): Faecal occult blood test positive; SSL: Sessile serrated lesion; SSL-DR: Sessile serrated lesion detection rate; N/A: Not applicable.

Polypectomy findings

Histological assessment of all polypectomy samples revealed tubular adenomas as the most common finding (48.5%), followed by non-dSSLs (20.4%) and hyperplastic polyps (14.4%). Malignancy was identified in 11 of 3766 samples (0.3%), each from a distinct patient, representing 0.76% of the 1450 patients studied. The dSSLs were diagnosed in 14 samples (0.4%), each from unique patients (0.97% of total patients), and constituted 1.8% of all SSLs. Among the 14 patients with dSSLs, 3 had pre-existing SPS diagnoses, 2 received new SPS diagnoses, and 9 had no SPS diagnosis. The mean age for dSSL detection (72.5 years) was notably higher than for non-dSSL detection (65.05 years). Of all samples, 12.3% were within normal limits and 1.3% were inadequate for assessment. Notably, no villous adenomas were identified. Among the 237 patients (16.34%) without any polypectomy, only 3 had documented incomplete colonoscopies (Table 4).

Table 4 Polypectomies by location and findings, n (%).

Finding	Location										Overall (n = 3749)
	Caecum (n = 385)	Ascending colon (n = 740)	Hepatic flexure (n = 45)	Transverse colon (n = 1371)	Splenic flexure (n = 5)	Descending colon (n = 298)	Sigmoid colon (n = 722)	Rectosigmoid junction (n = 6)	Rectum (n = 175)	Unknown (n = 2)
Normal	54 (14.0)	117 (15.8)	2 (4.4)	206 (15.0)	0 (0)	25 (8.4)	52 (7.2)	0 (0)	6 (3.4)	0 (0)	462 (12.3)
TA	211 (54.8)	427 (57.7)	32 (71.1)	660 (48.1)	1 (20.0)	124 (41.6)	318 (44.0)	1 (16.7)	44 (25.1)	0 (0)	1818 (48.5)
TVA	16 (4.2)	9 (1.2)	1 (2.2)	11 (0.8)	1 (20.0)	3 (1.0)	34 (4.7)	1 (16.7)	11 (6.3)	0 (0)	87 (2.3)
HP	14 (3.6)	31 (4.2)	3 (6.7)	163 (11.9)	1 (20.0)	66 (22.1)	168 (23.3)	2 (33.3)	89 (50.9)	1 (50.0)	538 (14.4)
SSL	85 (22.1)	141 (19.1)	6 (13.3)	303 (22.1)	2 (40.0)	68 (22.8)	135 (18.7)	0 (0)	23 (13.1)	0 (0)	763 (20.4)
dSSL	1 (0.3)	1 (0.1)	0 (0)	8 (0.6)	0 (0)	2 (0.7)	2 (0.3)	0 (0)	0 (0)	0 (0)	14 (0.4)
TSA	0 (0)	0 (0)	0 (0)	1 (0.1)	0 (0)	2 (0.7)	3 (0.4)	1 (16.7)	0 (0)	0 (0)	7 (0.2)
Malignancy	0 (0)	5 (0.7)	0 (0)	1 (0.1)	0 (0)	0 (0)	2 (0.3)	1 (16.7)	1 (0.6)	0 (0)	10 (0.3)
Inadequate sample	4 (1.0)	9 (1.2)	1 (2.2)	18 (1.3)	0 (0)	8 (2.7)	8 (1.1)	0 (0)	1 (0.6)	0 (0)	49 (1.3)
Lost	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	1 (50.0)	1 (0.0)

Normal: Reflects samples within normal limits; TA: Tubular adenoma; TVA: Tubulovillous adenoma; HP: Hyperplastic polyp; SSL: Sessile Serrated lesion; dSSL: Dysplastic sessile serrated lesion; TSA: Traditional serrated adenoma; Malignancy: Encompasses cancerous findings; Inadequate sample; Samples insufficient for histological assessment, for example, acellular samples or those with only faecal matter; Lost: Reflects samples that were lost in the handling process and were not received for histopathological assessment.

Detection rates by indication

Across all colonoscopy indications, the overall polypectomy rate was 83.66%, with an adenoma detection rate (ADR) of 57.03%, proximal serrated detection rate of 37.1%, serrated polyp detection rate of 30.97%, and SSL-DR of 30.69%. SSL-DR after excluding both IBD and SPS patients (n = 1282): SSL-DR: 28.78%. The faecal occult blood test positive (FOBT)-positive cohort demonstrated the highest ADR at 81% and highest SSL-DR at 42%, while the clinical symptoms cohort showed the lowest rates (ADR: 51.31%, SSL-DR: 24.34%). Notably, all detection metrics consistently followed this pattern, with the FOBT-positive group having the highest rates and the clinical symptoms group the lowest, while patients undergoing surveillance for previous findings consistently displayed the second-lowest detection rates across all metrics (Table 5).

Table 5 Polypectomy and detection rates by indication.

Indication	Proportions (%)
	Polypectomy rate	ADR	ASLDR	PSDR	SPDR	SSL-DR
Overall (n = 1450)	83.66	57.03	48	37.1	30.97	30.69
Clinical symptoms (n = 419)	75.1	51.31	39.38	29.83	24.34	24.34
FOBT (+) (n = 100)	90	81	58	43	43	42
Surveillance (previous patient) (n = 792)	86.49	56.19	49.62	38.64	31.94	31.69
Surveillance (new patient) (n = 74)	87.84	63.51	55.41	45.95	39.19	39.19
Screening (n = 65)	89.23	60	60	46.15	33.85	32.31

FOBT (+): Faecal occult blood test positive; Polypectomy rate: The proportion of colonoscopies during which at least one polypectomy was performed; ADR: Adenoma detection rate; ASLDR: Any serrated lesion detection rate; SPDR: Serrated polyp detection rate; PSDR: Proximal serrated detection rate; SSL-DR: Sessile serrated lesion detection rate.

The adjusted odds ratios for predictor variables in the final multivariate model are presented in Figure 1; these parameters provide adjusted probability estimates for SSL detection stratified by clinical indication, bowel preparation quality, age at colonoscopy, sex, IBD status, SPS status, and endoscopist. The odds of SSL detection were significantly elevated among patients whose primary indication was a positive FOBT [odds ratio (OR) = 2.30, 95%CI: 1.20-4.40, P = 0.004). Similarly, compared to patients undergoing surveillance colonoscopy for previous pathology, the FOBT-positive cohort demonstrated 1.87-fold greater odds of SSL detection (95%CI: 1.02-3.43, P = 0.039).

Figure 1 Forrest plot of variables associated with sessile serrated lesion detection. SSL: Sessile serrated lesion; OR: Odds ratio; CI: Confidence interval; SPS: Serrated polyposis syndrome; IBD: Inflammatory bowel disease; FOBT: Faecal occult blood test positive.

Bowel preparation quality exhibited a significant association with SSL-DRs. Compared to subjects with inadequate bowel preparation, those with adequate preparation demonstrated substantially higher odds of SSL detection (OR = 2.58, 95%CI: 1.12-5.94, P = 0.021), with a similar effect observed for good preparation quality (OR 2.43, 95%CI: 1.08-5.46, P = 0.027). The presence of SPS markedly increased the likelihood of SSL detection, with patients having either new or established SPS diagnoses exhibiting 3.72-fold higher odds compared to non-SPS subjects (95%CI: 2.47-5.61, P < 0.001). Notably, patients without IBD demonstrated significantly higher odds of SSL detection compared to those with IBD (OR = 2.33, 95%CI: 1.07-5.07, P = 0.032; Table 6).

Table 6 Polypectomy and detection rates by indication.

Comparisons	Statistics
	OR	95%CI	P value
Indication
FOBT (+)/clinical symptoms	2.299	1.203-4.396	0.004a
Surveillance (previous patient)/clinical symptoms	1.229	0.829-1.824	0.610
FOBT (+)/surveillance (previous patient)	1.870	1.02-3.43	0.039a
Surveillance (new patient)/clinical symptoms	1.898	0.912-3.953	0.120
FOBT (+)/surveillance (new patient)	1.211	0.508-2.888	0.975
Surveillance (new patient)/surveillance (previous patient)	1.544	0.767-3.108	0.437
Screening/clinical symptoms	1.386	0.625-3.073	0.797
FOBT (+)/screening	1.659	0.656-4.194	0.570
Screening/surveillance (previous patient)	1.128	0.52-2.444	0.993
Surveillance (new patient)/screening	1.370	0.51-3.679	0.909
Bowel preparation status
Adequate/inadequate	2.578	1.119-5.939	0.021a
Good/inadequate	2.430	1.082-5.458	0.027a
Adequate /good	1.061	0.748-1.504	0.917
Serrated polyposis syndrome status (grouped diagnoses)
SPS diagnosis (new or prior)/SPS absent	3.723	2.473-5.606	< 0.001a
Inflammatory bowel disease status
IBD absent/IBD present	2.332	1.073-5.065	0.032a
Endoscopist
Endoscopist 1/endoscopist 2	1.43	1.01-2.02	0.043a
Patient sex
Male/female	1.021	0.805-1.296	0.861

^aP values < 0.05.

Comparisons are made such that all odds ratios are greater than 1 for ease of interpretation odds ratios > 1 for ease of interpretation. OR: Odds ratio; CI: Confidence interval; FOBT (+): Faecal occult blood test positive; IBD: Inflammatory bowel disease.

This multivariate analysis demonstrated statistically significant associations between SSL-DRs and several key variables: Colonoscopy indication, IBD status, SPS diagnosis, endoscopist identity, and bowel preparation quality. Conversely, neither patient age nor sex demonstrated statistically significant associations with SSL detection in this cohort after controlling for other variables in the model.

DISCUSSION

This study aimed to contribute to the sparse Australian literature on SSL-DRs and factors associated with their variability. Unlike other countries with comprehensive colonoscopy registries, Australia lacks standardized SL reporting metrics and centralized data collection beyond the National Bowel Cancer Screening Program, which represents only approximately 5% of the more than 900000 colonoscopies performed annually[31].

The SSL-DR of 30.7% reported in this study substantially exceeds both international and Australian literature benchmarks. While Australia consistently demonstrates higher SSL-DRs compared to other regions[24,24], our findings remain notably elevated even within the Australian context. Comparable detection rates have been observed only among outlier European endoscopists and in an Asian study using high-dose bowel preparation, which reported an SSL-DR of 28%[28,29,32].

Several factors may contribute to this marked variation. While age-related differences in SSL detection have been suggested, Wong et al[11] found no statistically significant difference between age groups (2.3% in patients < 50 years; 3.4% in patients ≥ 50 years) - rates approximately ten times lower than our findings. Ethnicity may also influence SSL prevalence, with evidence suggesting higher rates among Caucasians, though such data was unavailable for comparison in our study[33]. The simplified World Health Organization diagnostic criteria for SSLs likely contributed to increased detection, though this effect appears too modest to explain the several-fold inter-study variation[13,17].

The indication for colonoscopy significantly influenced SSL-DR. While our overall pattern of detection across indications aligns with Bettington et al[17], our FOBT-positive cohort demonstrated a substantially higher SSL-DR (42% vs their 16.7%). This finding warrants further investigation, particularly given the implications for national screening programs.

Patients with SPS were overrepresented in our study (7.8%) compared to international estimates of approximately 1 in 111 in screening populations[33-35]. However, even after excluding SPS patients, our SSL-DR of 28.2% remains higher than typically reported. The lower SSL-DR observed among IBD patients aligns with limited existing evidence, though more research is needed to understand this relationship.

Endoscopist variation was observed and was statistically significant (31.6% vs 24.5%; OR = 1.43, 95%CI: 1.01-2.02, P = 0.043), with the caveat that endoscopist 2 had a considerably smaller sample size. Notably, both endoscopists achieved SSL-DRs substantially exceeding typical Australian reports. The use of the EndoCuff^® device by endoscopist 1 may have contributed to enhanced detection rates[34,35], though endoscopist 2 also achieved comparatively high rates without this device, suggesting that other factors beyond equipment may influence detection capability.

Regarding dSSLs, our finding that 1.8% of SSLs were dysplastic compares favorably with Zhang et al[1] reported 1.3%. Similarly, our per-patient dSSL-DR (0.97%) exceeds their 0.26%, despite similar SPS prevalence. The higher mean age for dSSL detection compared to non-dSSLs aligns with current understanding of the serrated neoplasia pathway[1]. While our study demonstrates exceptionally high SSL-DRs, it remains unclear whether this reflects a unique regional population with higher SSL prevalence or superior detection methods leading to greater ascertainment of SSLs and consequent SPS diagnoses. Further research with larger, diverse Australian cohorts is needed to resolve this question.

Significance of findings

This study addresses the significant knowledge gap regarding factors influencing SSL-DR variability in Australia, providing crucial insights into how patient demographics, clinical indications, and procedural factors affect detection outcomes. The exceptionally high SSL-DR of 30.7% observed in our regional centre dramatically exceeds previously reported Australian rates, further highlighting the unexplained inter-study variability in the literature. Given the established protective effect of higher SSL detection against PCCRCs, our findings underscore the urgent need for standardized reporting and quality benchmarks that can distinguish between appropriate clinical variations and those indicating suboptimal practice. The unprecedented detection rates among FOBT-positive patients (approximately 40%) warrant particular attention from screening program administrators. These results emphasize the importance of context-specific quality monitoring that accounts for clinical indications, bowel preparation quality, and patient comorbidities to ensure optimal cancer prevention outcomes across diverse Australian healthcare settings.

Study limitations

A key strength of this study was its comprehensive data acquisition methodology, which enabled robust statistical modelling of multiple factors potentially associated with SSL-DRs. This multivariable analysis allowed for better isolation of independent predictors while controlling for potential confounders.

Several methodological limitations warrant critical examination. Our single-center, retrospective study design inherently introduces constraints associated with observational research, including limitations regarding causal inference and external validity. The hierarchical indication classification system we employed, while pragmatically necessary, inevitably reduced the granularity of clinical data. This approach failed to capture patients presenting with multiple indications and consolidated diverse clinical presentations (abdominal pain, rectal bleeding, iron deficiency anemia, and abnormal imaging findings) that may exhibit heterogeneous associations with SSL prevalence. Furthermore, while we excluded repeat colonoscopies within the 2023 calendar year, our methodology did not identify patients who underwent colonoscopy in late 2022 with subsequent urgent follow-up in early 2023, potentially introducing selection bias. Based on our observed data patterns throughout 2023, this effect appears minimal but cannot be definitively excluded. Our study was limited by the absence of comprehensive data on certain patient-level risk factors, including smoking status, BMI, and family history of CRC, which may influence SSL development.

While all histopathological assessments were conducted by Douglas Hanley Moir Pathology with specialist gastrointestinal histopathologists verifying dSSL diagnoses, our study did not capture pathologist-specific SSL diagnosis rates. This remains an important gap in understanding the full spectrum of factors influencing SSL detection and diagnosis. The recent simplification of SSL diagnostic criteria has improved inter-observer agreement, but pathologist variability remains an understudied yet critical component of the diagnostic pathway. Future research should incorporate pathologist-specific data to more comprehensively understand the factors influencing SSL detection and diagnosis.

CONCLUSION

In conclusion, this study documents one of Australia's highest reported SSL-DRs at 30.7% across 1450 colonoscopies from a regional population, further highlighting the marked variability in Australian SSL-DRs. Notably, the FOBT-positive cohort demonstrated an unprecedented 40% SSL-DR, substantially exceeding previously reported rates. While our findings identify several factors associated with SSL detection variability, the substantial inter-study differences observed in the Australian literature remain largely unexplained, suggesting the need for standardized detection protocols and further investigation.

ACKNOWLEDGEMENTS

A/Professor Stuart Kostalas would like to acknowledge Professor Barabra Leggett for her support, ideas and suggestions. He would also like to acknowledge Professors Brian Nicholson and Professor Eva Morris for their ongoing research support.