Clinical Question

Are the modern fecal immunochemical tests (FIT) for occult blood in the stool less accurate in patients who are taking aspirin, an anticoagulant, or a nonsteroidal anti-inflammatory drug (NSAID)?

Bottom Line

The use of aspirin, NSAIDs, and oral anticoagulants has no clinically important effects on the positive predictive value of FIT in a screening population. (Level of Evidence = 1a)

Synopsis

Previous research has shown that approximately 6.2% of screening FIT results are positive, with a positive predictive value of 35% to 55%. The authors wondered whether the use of something that can make you bleed would reduce the positive predictive value by making benign lesions more likely to bleed (leading to more false-positive results), or whether it would increase the positive predictive value by making precancerous and malignant lesions more likely to bleed. They did a search of the literature and identified eight studies with 2,022 patients that compared the accuracy of FIT in a screening population of patients taking an oral anticoagulant or an NSAID with those not taking either drug. Of the eight studies, all but one were done in Europe (the eighth was in Hong Kong), and most used a FIT cutoff of 15 to 20 mcg hemoglobin per g. Six studies included aspirin users, four included oral anticoagulant users, and one included NSAID users (three of the studies included more than one medication). The authors found no consistent effect on positive predictive value among users and nonusers of oral anticoagulants and NSAIDs, and in general the differences were small. For example, the pooled positive predictive value for advanced neoplasia was 38.2% in aspirin and NSAID users and 39.4% in nonusers. The positive predictive values for colorectal cancer in oral anticoagulant users and nonusers were 5.7% and 6.2%, respectively. The positive predictive values for advanced neoplasia in oral anticoagulant users and nonusers were 37.6% and 40.3%, respectively.

Study design: Systematic review

Funding source: Self-funded or unfunded

Setting: Various (meta-analysis)

Reference: Nieuwenburg SA, Vuik FE, Kruip MJ, et al. Effect of anticoagulants and NSAIDs on accuracy of faecal immunochemical tests (FITs) in colorectal cancer screening: a systematic review and meta-analysis. Gut. 2019;68(5):866–872.

Editor's Note: Dr. Ebell is deputy editor for Evidence-Based Medicine for AFP and cofounder and editor-in-chief of Essential Evidence Plus, published by Wiley-Blackwell.