Evaluation of a fecal immunochemistry test prior to colonoscopy for outpatients with various indications

Abstract

Background: Stool tests can predict advanced neoplasms prior to colonoscopy. Results of immunochemical stool tests to predict findings at colonoscopy for various indications are less often reported. We compared pre-colonoscopy stool tests with findings in patients undergoing colonoscopy for different indications.

Patients and methods: Charts of patients undergoing elective or semi-urgent colonoscopy were reviewed. Comparison of adenoma detection rates and pathological findings was made between prescreened and non-prescreened, and between stool-positive and stool-negative cases. Demographics, quality of colonoscopy, and pathological findings were recorded. Odds ratios (ORs) and 95% confidence intervals (CIs) were assessed. Statistical significance was accepted at p≤0.05.

Results: Charts of 325 patients were reviewed. Among them, stool tests were done on 144 patients: 114 were negative and 30 were positive. Findings were similar in the pretest and non-pretest groups. Detection of advanced adenomas per patient was higher in the stool-positive group compared to the stool-negative group (23.4% vs 3.5%, p=0.0016, OR =7.6 [95% CI: 2-29.3]). Five advanced adenomas (without high-grade dysplasia or adenocarcinoma) and several cases of multiple adenomas were missed in the negative group. Sensitivity and specificity for advanced polyps was 63.6% and 82.7%, respectively. The negative predictive value was 96.5%. Male gender was independently predictive of any adenoma.

Conclusion: The stool immunochemical test best predicted advanced neoplasms and had a high negative predictive value in this small cohort. Whether this test can be applied to determine the need for colonoscopy in groups other than average risk would require more studies.

Keywords: blood; colonoscopy; fecal; outcome; risks.

Figure 1

The total number of colonoscopies, included and excluded cases for a 21-month period. Notes: The indication “screen” includes all patients without any symptoms. This includes average risk, family history of adenomas or adenocarcinoma of the colorectum, previous finding of adenomas or colorectal cancer on previous colonoscopy as well as seven cases sent for colonoscopy because of positive FIT alone. The indication “symptoms” includes all symptoms including rectal bleeding, iron deficiency (with or without anemia), abdominal pain, change in bowel pattern, diarrhea (but not chronic constipation), or weight loss. Abbreviation: FIT, fecal immunochemistry test; IBD, inflammatory bowel disease.