# Correlation of Pre-colonoscopy Blood Hemoglobin Levels With Significant Colorectal Pathology Among Fecal Immunochemical Test-Positive Patients

## TL;DR

This study found no strong link between blood hemoglobin levels and colorectal cancer in patients with positive fecal tests, suggesting hemoglobin alone cannot predict cancer risk.

## Contribution

The study provides evidence that pre-colonoscopy hemoglobin levels are not reliable indicators of significant colorectal pathology in FIT-positive patients.

## Key findings

- Median hemoglobin levels did not significantly differ across colorectal pathology groups.
- Most patients with colorectal cancer had normal hemoglobin levels.
- Hemoglobin cannot reliably predict the presence of advanced colorectal neoplasia.

## Abstract

Background

Fecal immunochemical testing (FIT) is a widely implemented noninvasive screening tool for colorectal cancer (CRC). While FIT detects occult gastrointestinal (GI) bleeding, the relationship between systemic blood hemoglobin (Hb) levels and significant colorectal pathology (SCP) among FIT-positive patients remains uncertain. Identifying such an association could improve clinical triage and resource allocation in screening programs.

Methodology

This retrospective observational study was conducted at Prince Sultan Military Medical City, Riyadh, Saudi Arabia. All adults (≥18 years) who tested positive on FIT and subsequently underwent complete colonoscopy between December 2024 and September 2025 were included. Patients with incomplete colonoscopy, inadequate bowel preparation, missing Hb data, active non-colorectal GI bleeding, hematologic disorders, or prior colorectal surgery or malignancy were excluded. Pre-colonoscopy Hb was obtained within 12 weeks of colonoscopy. SCP was defined as tubular adenoma, tubulovillous adenoma, or adenocarcinoma. Hb levels were compared across pathology groups using the Kruskal-Wallis test, and anemia prevalence was analyzed using the chi-square test.

Results

Among 483 FIT-positive patients, 182 met the inclusion criteria. The mean age was 59.3 ± 11.8 years, and 55% were male. The median pre-colonoscopy Hb level was 13.9 g/dL (interquartile range (IQR) 12.7-15.0). Histopathology revealed tubular adenoma in 89 (48.9%), tubulovillous adenoma in 35 (19.2%), adenocarcinoma in 23 (12.6%), hyperplastic polyps in 16 (8.8%), and other benign lesions in 19 (10.4%). Median Hb differed slightly across groups, lowest in adenocarcinoma (12.8 g/dL) and highest in benign lesions (14.8 g/dL), but the difference was not statistically significant (P = 0.245). Overall, 139 (76%) patients, including 78% with adenocarcinoma, had normal Hb levels.

Conclusions

No significant correlation was observed between pre-colonoscopy blood hemoglobin and SCP among FIT-positive patients. Most individuals with advanced neoplasia had normal Hb concentrations, indicating that systemic hemoglobin is not a reliable predictor of malignancy in this population. Normal Hb should not be considered reassuring and must not delay colonoscopic evaluation following a positive FIT result.