Using CT colonography as a triage technique after a positive faecal occult blood test in colorectal cancer screening

Abstract

Objective:The purpose of this study was to evaluate the effectiveness of CT colonography (CTC) as a triage technique in faecal occult blood test (FOBT)-positive screening participants.Methods:Consecutive guaiac (G-FOBT) and immunochemical (I-FOBT) FOBT-positive patients scheduled for colonoscopy underwent CTC with iodine tagging bowel preparation. Each CTC was read independently by two experienced observers. Per patient sensitivity, specificity and positive and negative predictive values (PPV and NPV) were calculated based on double reading with different CTC cut-off lesion sizes using segmental unblinded colonoscopy as the reference standard. The acceptability of the technique to patients was evaluated with questionnaires.Results:302 FOBT-positive patients were included (54 G-FOBT and 248 I-FOBT). 22 FOBT-positive patients (7%) had a colorectal carcinoma and 211 (70%) had a lesion ⩾6 mm. Participants considered colonoscopy more burdensome than CTC (p<0.05). Using a 6 mm CTC size cut-off, per patient sensitivity for CTC was 91% (95% CI 85% to 91%) and specificity was 69% (95% CI 60% to 89%) for the detection of colonoscopy lesions ⩾6 mm. The PPV of CTC was 87% (95% CI 80% to 93%) and NPV 77% (95% CI 69% to 85%). Using CTC as a triage technique in 100 FOBT-positive patients would mean that colonoscopy could be prevented in 28 patients while missing ⩾10 mm lesions in 2 patients.Conclusion:CTC with limited bowel preparation has reasonable predictive values in an FOBT-positive population and a higher acceptability to patients than colonoscopy. However, due to the high prevalence of clinically relevant lesions in FOBT-positive patients, CTC is unlikely to be an efficient triage technique in a first round FOBT population screening programme.

Sensitivity and specificity of CT colonography for the detection of colonic neoplasia after positive faecal occult blood testing: systematic review and meta-analysis

“…Five articles were included, reporting four distinct studies [26][27][28][29][30]. Two of these articles reported different primary outcome measures for the same patient cohort [26,27].…”

Role of CT colonography in screening programs

“…CTC was confirmed as having sensitivities comparable to colonoscopy for polyps larger than 5 mm. The debate of whether CTC may be used in FOBT-positive subjects is still open, as recent data [89] have demonstrated that CTC in this setting had good predictive values and a higher acceptability than colonoscopy. The results of some of the aforementioned screening trials are shown in Table 2.…”

Do prevalence expectations affect patterns of visual search and decision-making in interpreting CT colonography endoluminal videos?

“…It is possible that the expected prevalence level needs to be ,20% for an effect to be visible, as is usually the case in everyday clinical practice, except in very high-risk patient groups such as those examined following a positive faecal occult blood test. 21 Evans et al 8 found a marked reduction in sensitivity for breast cancer diagnosis using mammography during screening when the prevalence was extremely low (0.3%). Whether a similar effect applies to CTC remains unknown.…”

“…Navigation speed was fixed at approximately 1.5 cm s 21 . Five videos depicted a single colorectal polyp (true positive, 5-8 mm maximal transverse dimension), verified by three radiologists with .200 cases' experience.…”

“…3 This is surprising because CTC is commonly applied across a wide range of expected prevalence, from asymptomatic individuals undergoing screening [16][17][18] to symptomatic and high-risk patients. [19][20][21] Establishing the presence or absence of a prevalence effect on reader attention, visual search and diagnostic performance is important both in understanding how CTC should be used in clinical practice and for designing future research studies.…”