Introduction

Colonoscopy is without dispute the gold standard for clinical evaluation of the colon.¹ However its effectiveness as a tool for the detection of significant neoplastic lesions, (adenomas and cancers) – here referred to as “SNL”, has been shown to be closely correlated with several key performance indicators. These form the basis of current screening guidelines and include: 1). Caecal Intubation rate², 2). Adequacy of bowel preparation³ and 3). Withdrawal time to anus^4-5.

A caecal intubation rate of ≥ 90% is the recommended standard by the U.S. Multi-Society Task Force on Colorectal Cancer among other advisory bodies⁶, while published rates vary widely from 55-98.8%². Successful caecal intubation has been shown to be heavily dependent on the clinical experience of the operator^7-8; although factors independent of the operator may limit outcomes including previous pelvic surgery, female gender and a long transverse colon^9-10. Longer withdrawal times furthermore are associated with higher adenoma detection rates (ADR) after adjustment of other variables, with the U.S. Multi Society Task Force on Colorectal Cancer recommending a minimum of 6-10 minutes; that being the mean time for operators with low rates of missed adenomas^{4 11-12}. The Task Force (2002) also recommended a benchmark ADR of 25% for males and 15% for females over 50¹³.

We evaluated colonoscopies undertaken at the endoscopic unit of a rural general hospital for: 1). SNL detection rate (including ADR). 2). Caecal intubation rate, 3). Adequacy of bowel preparation and 4). Withdrawal time to anus. Secondly, we evaluated SNL detection rates for different colonoscopic indications with relevance to the wider body of knowledge contributing to the sometimes difficult question of when to screen.

Patients and Methods

Data Retrieval

Patients

Bowel Preparation

Procedures

Results

Demographics

371 patients received colonoscopies (163 male, 208 female) for 453 indications. The vast majority were in age categories 41-60 and 61-80.

Figure 1

Endoscopic Findings

153 procedures (41%) were normal. 77 polyps were detected in 73 patients of which 52 were adenomas. 15 cancers were detected in 15 patients, all adenocarcinomas. Diverticular Disease was detected in 99 patients (26.7%)

Figure 2

Colonoscopy Key Performance Indicators

ADR fell short of benchmark standards at 11.86% of procedures overall (males 18.4%, females 6.7%). Inclusion of cancers (SNL detection rate) yielded 15.9% (males 20.86%, females 12.02%) with a statistically significantly higher proportion for males (p < 0.0001), whereas there were no significant differences in SNL detection rates between age categories of 21-40, 41-60, 61-80, >80 (p = 0.3145)

Figure 3

Overall caecal intubation rate was 85.6% (males 90.5%, females 81.4%) not including those not recorded (0.9%). Most common causes for failure were poor bowel preparation (n = 18), obstructing mass/stricture (n = 9) and excessive bowel looping or difficult angulation (n = 9).

Figure 4

Figure 5

Bowel preparation was judged as adequate in 79.24% (good = 56.87 %, fair = 22.37%), poor = 13.4%, not recorded = 7.28%.

Figure 6

Mean withdrawal time to anus was 5.76 minutes. ADR for withdrawal time categories of 0-5, 6-10 and > 11 minutes were compared defining ADR as number of lesions detected rather than positive procedures yielding adenomas (or SNL) consistent with previous studies^{4 11-12}. There were no significant differences in male: female ratio (p = 0.3749) or the major colonoscopic indications listed in Table 5 (p = 0.9614) between categories. Withdrawal times of 6-10 and >11 minutes yielded greater ADR than 0-5 minutes (p<0.0001) with no differences between the two longer categories (p = 0.1714). All patients with multiple adenomas (6 patients with 12 adenomas) were in the longer time categories.

Figure 7

SNL detection rates according to indication

Below we compare Number Needed to Screen (NNS) for detection of SNL against colonoscopic indication using X ² univariate analysis. PR bleeding, change in bowel habit, family history of colorectal cancer and positive Faecal Occult Blood all showed high diagnostic yield. For each indication category there were no significant differences in sex ratio (p = 0.5186).

Figure 8

Discussion

Colonoscopy, alongside Faecal Occult Blood testing has been shown to lower mortality. The Australian Institute of Health and Welfare (AIHW) statistics for 2006 listed Colorectal Cancer as the second most common cause of cancer at an annual incidence of 13.1% of all newly diagnosed cancers¹⁵. Similarly, 9.7% of all mortality attributable to cancer was due to colorectal cancer¹⁶. Detection of adenomas remains a good surrogate for malignancy, with a 5% transformation rate¹⁷. ADR in our study fell below benchmark standards, especially in women; although the wide range of ADR in the literature must be appreciated.

ADR is subject to numerous variables. Male sex as shown in our study is a recognised independent risk factor¹¹. Notably our study had a higher proportion of female participants. There were no statistically significant differences across age categories; although the majority of studies point to age being an independent risk factor¹⁸. Adequacy of bowel preparation ranked reasonably well at 79.24% alongside a 77% adequacy rate found across 93,004 cases in the US¹⁹ without including 7.28% of cases for which quality of bowel preparation was not recorded. Importantly, the semi-subjective nature of assessing quality of bowel preparation must be recognised, especially given that no universally-recognised system for evaluating quality of bowel preparation exists¹⁹.

Our finding of lower ADR at withdrawal times 0-5 minutes is significant and consistent with a wide body of literature¹². Importantly we have accounted for the confounding effects of sex ratio and relative proportions of screening indications on withdrawal time categories. Similarly, all patients with multiple adenomas detected belonged to longer withdrawal time categories. The significance of the latter point is uncertain, but it may be speculated that initial detection of adenomas may cause the endoscopist to slow down. However, an important confounder to higher ADR at longer withdrawal times is the time taken to snare polyps during withdrawal which intuitively would increase with number of polyps detected. Importantly we have not recorded for adenoma size. The malignant potential of adenomas < 10 mm remains controversial²⁰.

Few studies have been performed comparing the diagnostic yield of presenting indications. Importantly there was a large amount of overlap with 453 indications across the 371 patients, especially for abdominal pain and PR bleeding. Our findings were somewhat comparable to a significantly larger Dutch trial¹⁸ (n = 4623) which found SNL detection rates of 15% for PR bleeding; 21% for abdominal pain and/or change in bowel habit; 8% for Anaemia; 10% for past history of Colorectal Cancer and 13% for past history of polyps. Significantly their SNL detection rate for family history of colorectal cancer was 10% compared to our finding of 20.69%. Faecal Occult Blood remains a useful screening tool for asymptomatic patients with published meta-analyses showing reduction in mortality from colorectal cancer by 14-16%^21-22; hence the federal initiative (2006) of the largely successful National Bowel Screening Program with detection rates of 5.2% for cancers and 12.4% for adenomas²³.