Objective: To evaluate the effectiveness of CT colonography (CTC) as a triage technique in Faecal Occult Blood Test (FOBT) positive screening participants.
Methods: Consecutive guiac (G-FOBT) and immunochemical (I-FOBT) FOBT positives 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. Patient acceptance was evaluated with questionnaires.
Results: 302 FOBT positives were included (54 G-FOBT and 248 I-FOBT). 22 FOBT positives (7%) had a colorectal carcinoma and 211 (70%) had a lesion ≥6mm. Participants considered colonoscopy more burdensome than CTC (p<0.05). Using a 6mm 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 ≥6mm. 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 positives would mean that colonoscopy could be prevented in 28 patients while missing ≥10mm lesions in 2 patients.
Conclusion: CTC with limited bowel preparation has reasonable predictive values in a FOBT positive population and a higher patient acceptation than colonoscopy. But due to the high prevalence of clinically relevant lesions in FOBT positives, CTC is unlikely to be an efficient triage technique in a first round FOBT population screening programme.