Anticoagulant or aspirin treatment does not affect the positive predictive value of an immunological fecal occult blood test in patients undergoing colorectal cancer screening: results from a nested in a cohort case-control study.

Background And Aim: The immunochemical fecal occult blood test (i-FOBT) is widely used as a recommended screening strategy for colorectal cancer (CRC). A growing number of patients potentially targeted by CRC screening programs are on oral anticoagulant or chronic low-dose aspirin therapy, mainly for primary or secondary cardiovascular prophylaxis. This study aims at evaluating whether the use of these medications may impact on the diagnostic performances of i-FOBT for CRC screening.

Methods: All i-FOBT-positive patients on anticoagulant or chronic low-dose aspirin therapy recorded in a regional mass screening program database were enrolled as cases. Control groups were derived from the same database and included drug-naive i-FOBT-positive patients, matched in a ratio of 1 : 2 for age (± 3 years of age), sex, date of colonoscopy, and practice site. Information about the use of medications was collected by cross-checking patients' interview before colonoscopy and data recorded in the provincial electronic registry of medical prescriptions. The positive predictive value of i-FOBT for significant neoplasia (high-risk adenoma and CRC) was calculated in the case and control groups.

Results: In a 2-year study period, 2376 patients were recorded in the regional database. Of these patients, 53 (2%) were on anticoagulation (control group of 106 patients) and 172 (6.6%) were on chronic low-dose aspirin treatment (control group of 344 patients). Significant neoplasia was detected in 15 (28.3%) patients on anticoagulants and in 37 (34.9%) corresponding controls (P=0.45). Significant neoplasia was detected in 50 (29.1%) patients on chronic low-dose aspirin and in 107 (31.1%) corresponding controls (P=0.64).

Conclusion: The positive predictive value of i-FOBT for significant neoplasia is not affected by ongoing anticoagulant or chronic low-dose aspirin therapy. This finding suggests that there is no need to interrupt these treatments before i-FOBT for CRC screening.