Using CT colonography as a triage technique after a positive faecal occult blood test in colorectal cancer screening
- M H Liedenbaum1,
- A F van Rijn1,
- A H de Vries1,
- H M Dekker2,
- M Thomeer3,
- C J van Marrewijk3,
- L Hol3,
- M G W Dijkgraaf1,
- P Fockens1,
- P M M Bossuyt1,
- E Dekker1,
- J Stoker1
- 1Academic Medical Centre Amsterdam, The Netherlands
- 2Radboud University Nijmegen Medical Centre, The Netherlands
- 3Erasmus Medical Centre Rotterdam, The Netherlands
- Correspondence to Mrs M H Liedenbaum, Department of Radiology, G1-226, Academic Medical Centre, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands;
- Revised 31 March 2009
- Accepted 1 April 2009
- Published Online First 21 July 2009
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.
Funding Supported by The Netherlands Organization for Health Research and Development (ZonMW: project number 62300036)
Competing interests None.
Ethics approval The CTC study was approved by the institutional review boards of the three institutions involved in the study.