A0169 - What Do "False-Positive" Stool Tests Really Mean? Data From the New Hampshire Colonoscopy Registry

Award: Presidential Poster Award

Lynn F. Butterly, MD¹, Christina Robinson, MS², William Hisey, MSc³, Paul Limburg, MD, MPH⁴, Bonny Kneedler, MS⁵, Joseph C. Anderson, MD^3
1Dartmouth Hitchcock, Hanover, NH; ²Dartmouth Hitchcock, Lebanon, NH; ³Dartmouth, Hanover, NH; ⁴Mayo Clinic, Rochester, MN; ⁵Exact Sciences, Madison, WI

Introduction: Accurate understanding of the frequency of meaningful ‘true positive’ and ‘false positive’ mt-sDNA and FIT results is essential to optimizing the use of these important, common colorectal cancer (CRC) screening tests. We utilized the statewide, population-based New Hampshire Colonoscopy Registry (NHCR) to investigate colonoscopy outcomes using 3 distinct definitions of a ‘positive’ colonoscopy, and present the corresponding false discovery rate and positive predictive values (PPV).

Methods: Data from Exact Sciences Laboratories and the NHCR identified patients with mt-sDNA+ tests followed by colonoscopy resulting from routine care (8/15-12/20). We calculated false discovery rates (FDR) (# positive stool tests with negative colonoscopy divided by all positive stool tests) and the corresponding PPVs for both mt-sDNA+ and FIT+ cohorts using 3 definitions of positive colonoscopy:

1) Detection of colorectal advanced adenomatous Polyps and Cancer: DeeP-C Study (CRC, adenomas >1 cm or with 25%+ villous elements, high grade dysplasia or any serrated polyp [traditional serrated adenoma, sessile serrated polyp (SSP) or hyperplastic polyp (HP)] >1 cm)

2) Polyps requiring < 10 year follow up per USMSTF guidelines: includes DeeP-C findings (above) and 1 or more SSPs < 1 cm (with/without dysplasia) or 1 or more tubular adenomas < 1 cm.

3) Clinically Significant: Above DeeP-C and USMSTF findings and the remaining clinically significant serrated polyps: 5-9 mm proximal HPs.

Results: When using the strictest definition of positive colonoscopy, DeeP-C, the FDR was 71.9% for mt-sDNA+ and 81.7% for FIT+. Using the USMSTF definition, the FDR decreased to 33.2% for mt-sDNA+ and 47.6% for FIT+. Finally, adding 5-9 mm proximal HPs to the USMSTF < 10 year definition resulted in the lowest FDRs: 32.2% for mt-sDNA+ and 47.1% for FIT+ results. These decreasing FDRs correspond to increasing PPVs of 28.1% for mt-sDNA+ and 18.3% for FIT+ (DeeP-C) to 67.8% for mt-sDNA+ and 52.9% for FIT+ (DeeP-C + USMSTF + CSSP, Table 1).

Discussion: Our analysis demonstrates a substantial decrease in FDRs (and corresponding increases in PPV) when using a definition of positive colonoscopy that includes additional significant precancerous findings such as adenomas or SSPs. These data present a more comprehensive and clinically relevant understanding of false positive outcomes at colonoscopies following positive stool tests, and to our knowledge this is the first such assessment of these outcomes.





Disclosures:


Lynn F. Butterly, MD¹, Christina Robinson, MS², William Hisey, MSc³, Paul Limburg, MD, MPH⁴, Bonny Kneedler, MS⁵, Joseph C. Anderson, MD³. A0169 - What Do "False-Positive" Stool Tests Really Mean? Data From the New Hampshire Colonoscopy Registry, ACG 2022 Annual Scientific Meeting Abstracts. Charlotte, NC: American College of Gastroenterology.