Does the Value of the Faecal Immunochemical Test (FIT) Result Matter, and Can This Be Used as a Triage Criterion for Symptomatic FIT-Positive Patients?

TL;DR

This study explores whether the value of a positive FIT test can help prioritize patients for colon cancer investigations, finding that while high FIT values are more likely to indicate cancer, low values still require caution.

Contribution

The study evaluates the use of FIT test values as a triage tool for symptomatic patients, providing insights into how different FIT ranges correlate with cancer likelihood.

Findings

All 25 colorectal cancers were found in FIT-positive patients, with 52% having FIT values >400.

20% of cancers occurred in patients with low FIT values (11-50 µg/g), indicating low values are not entirely reassuring.

The positive predictive value of FIT for cancer was 11.2%, showing high FIT scores do not always indicate malignancy.

Abstract

Background

The Faecal Immunochemical Test (FIT) is a cornerstone in both colorectal cancer (CRC) screening programs and referral pathways for symptomatic patients. The test identifies haemoglobin in stool and, when present, is used as a referral indicator on the suspected CRC pathway. Since its introduction, the number of referrals with a positive FIT has risen, stretching diagnostic capabilities to the limit. This study examines whether the value of the result is significant and, if so, can be used as part of the triage process.

Methods

This retrospective cohort study analysed patients who underwent FIT as part of a CRC screening program between June 2020 and November 2021 in Wrightington, Wigan and Leigh NHS Foundation Trust. A total of 293 patients contributed clinical data, including FIT scores, presenting symptoms, and diagnostic outcomes. The patients were stratified according to ranges of FIT scores (<10, 11-50, 51-100, 101-150, 151-200, >400). Their correlating outcomes, including the presence of cancer, benign findings (e.g., polyps and diverticular disease), and inflammatory conditions (e.g., colitis), were recorded.

Results

Out of the 293 patients included in the study, 223 were FIT-positive and 70 FIT-negative, with 20 refusing investigations in the FIT-negative group and six in the FIT-positive group.

Among the investigated patients, 25 were diagnosed with CRC; all cases were in the FIT-positive group, and none were found in the FIT-negative group. The sensitivity of FIT for CRC detection was 100% (95% CI: 86.7-100%), and the negative predictive value (NPV) was 100% (95% CI: 94.8-100%), confirming FIT's strength as a rule-out test in this cohort. The positive predictive value (PPV) of a positive FIT result for CRC was 11.2% (95% CI: 7.4-15.9%).

Of the 25 cancers, 13 (52%) had a FIT value of >400, and five (20%) had a FIT value of 11-50. In this cohort, 76% of CRC were in the sigmoid or rectum, with 63% of these cases associated with FIT values >400 and 15% falling within the lower FIT range of 11-50.

For the remaining FIT-positive patients without cancer, 123/198 (62.1%) had a FIT value of 11-50. Of these, 63 (51.2%) had either a polyp, diverticular disease, or colitis. Of the remaining cancer-negative patients, 30/198 (15.2%) had a FIT value of >400, of which 22 (73%) had benign pathology. When symptoms were analysed, most patients had a change in bowel habit, with rectal bleeding being the most typical symptom in the cancer group.

Conclusions

FIT is used widely to aid referral for investigating symptoms suggestive of bowel cancer. As more patients are being referred with positive FIT, there is a need to try to rationalise investigations. The premise of this study was to determine whether a low FIT value corresponded with a low chance of finding a cancer in symptomatic patients, thus aiding the triage process, reducing the numbers having unnecessary investigations, and relieving the burden on endoscopy units.

In this particular study, none of the FIT-negative patients had bowel cancer, confirming FIT's strong rule-out performance. However, as 20% of cancers occurred among patients with low-positive FIT results (11-50 µg/g), clinicians should remain cautious in interpreting low values as entirely reassuring. While most cancers were seen with FIT >400, PPV remained low overall (~11%), and high FIT scores did not always indicate malignancy.

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