Blood in stool

In a prospective study of 593 patients at increased risk of colorectal cancer undergoing surveillance colonoscopy, 41 (6.9%) had advanced neoplasia (4 CRC, 37 higher-risk adenoma). Among 238 patients (40.1%) with detectable faecal haemoglobin (f-Hb ≥2 µg Hb/g faeces), 31 (13.0%) had advanced neoplasia compared with only 10 (2.8%) of 355 patients with undetectable f-Hb. Detectable f-Hb achieved a negative predictive value of 99.4% for colorectal cancer and 97.2% for colorectal cancer plus higher-risk adenoma. Median patient age was 64 years (IQR 55–71), with 54.6% male participants across two university hospitals (2014–2016).

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In a validation study of 5,660 primary care patients undergoing faecal immunochemical testing (FIT), 1,196 (41.7%) had faecal haemoglobin (f-Hb) ≥10 μg Hb/g faeces. Among 1,447 patients who underwent colonoscopy (group A), 296 had significant bowel disease (SBD) including colorectal cancer, advanced adenoma, or inflammatory bowel disease. Of those with SBD, 252 of 296 (85.1%) had elevated f-Hb ≥10 μg Hb/g faeces. The FAST score at a threshold >2.12 detected 286 of 296 (96.6%) with SBD but would have missed one CRC case, demonstrating that detectable faecal blood remains a critical warning sign for colorectal malignancy.

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This RCT of 48,888 subjects demonstrated that faecal haemoglobin detection via FIT identified advanced neoplasia with positive predictive values of 25.9% (OC-Sensor) and 25.6% (HM-JACKarc) among first-time screeners — meaning roughly 1 in 4 individuals with detectable faecal haemoglobin had colorectal cancer or advanced adenoma. Detection rates for advanced neoplasia were 1.40–1.42% at first screening and 0.83–0.96% at subsequent rounds. Among those with positive FIT results who underwent colonoscopy, the number needed to scope to detect one advanced neoplasia was as low as 3.9 (95% CI 2.9–5.8), underscoring the strong association between faecal blood and significant colorectal pathology.

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In a cohort of 30,893 screening participants aged 50-75 in the Scottish Bowel Screening Programme, 31 interval cancers (CRC diagnosed within two years of a negative FIT result) were identified alongside 30 screen-detected cancers, yielding an interval cancer proportion of 50.8%. Interval cancers presented at later stages: 46.7% were Dukes' stage C and 33.3% Dukes' stage D. Of the 31 interval cancers, 23 had faecal haemoglobin below 10 µg Hb/g, and 6 had undetectable levels. Even lowering the cut-off to 10 µg Hb/g would only reduce the interval cancer proportion to 38.3%, meaning 19.4% of cancers would still be missed.

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In a cohort of 1043 symptomatic primary care patients, 755 completed colonic investigations. Faecal haemoglobin was detectable in 57.6% of patients (median 0.4 µg/g, range 0–200). Among 103 patients with significant bowel disease, the negative predictive value of undetectable FHb was 100% for colorectal cancer, 97.8% for higher-risk adenoma, and 98.4% for IBD. The median age was 64 years (IQR 52–73), with 54.6% women. These diagnostic accuracy results from a blinded study design demonstrate that detectable faecal blood is a meaningful warning sign requiring further investigation.

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The pilot awareness campaign in two English regions in 2011 focused on increasing recognition of colorectal cancer signs and symptoms including rectal bleeding. Modeling based on the pilot data showed a 10% increase in presentation rates over one month. The lifetime horizon model predicted 66 prevented CRC deaths and 404 QALYs gained at £13,496 per QALY. The model incorporated changes in GP attendances, referrals, CRC incidence, stage distribution, and screening uptake, with results particularly sensitive to shifts in disease stage at diagnosis.

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In this 22-year screening study of 5,104 adults over 50, positive fecal occult blood tests led to colonoscopy that enabled early cancer detection. The three-tier screening protocol using guaiac-based and immunochemical fecal occult blood tests achieved 80.6% sensitivity (95% CI, 65.3-91.1) for detecting colorectal cancer. Among 57 total colorectal cancers identified across both groups, screening-detected cases had substantially better outcomes, with mortality reduced by 64% (relative risk 0.36, 95% CI 0.18-0.71) compared to cancers found without screening.

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In a retrospective cohort of 66 patients who underwent colonic resection for cancer over 58 months at Hospital Universitário da Universidade de São Paulo, hematoquezia (rectal bleeding) was the principal presenting symptom among the 28 patients in the elective surgery group. Elective group patients presented with more stage I cancers, whereas the 38 emergency surgery patients had more pT4 tumors. The majority of all patients had been symptomatic for months before surgery, indicating delayed diagnosis. Primary anastomosis was achieved in 81.8% of cases across both groups.

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Among 2,531 asymptomatic adults screened in this multicenter study, large adenomas and adenocarcinomas (≥10 mm) were identified with 90% sensitivity by CT colonography, confirmed against optical colonoscopy with histologic review. The 99% negative predictive value indicates that nearly all participants without detected lesions were truly disease-free. These findings demonstrate that significant colorectal neoplasms frequently exist without symptoms, reinforcing the clinical importance of investigating any warning signs such as rectal bleeding promptly.

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This RCT of 2,400 individuals aged 50–74 years focused on FIT-based colorectal cancer screening, which detects occult blood in faecal samples as a biomarker for CRC. Overall screening participation across the trial ranged from 36.0% to 48.3% depending on invitation strategy. The study was conducted within an organized community screening programme targeting the at-risk population (aged 50–74), underscoring that detection of faecal blood — whether through home testing or visible observation — is a critical early warning sign warranting prompt clinical follow-up for colorectal cancer.

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Clinical guideline with Strength of Recommendation A (based on high-quality systematic reviews of RCTs) identifies fecal blood detection as the cornerstone of colorectal cancer screening. The guideline confirms that FOBT reduces colorectal cancer mortality, underscoring that the presence of blood in stool — the very biomarker FOBT detects — is a clinically significant warning sign requiring medical follow-up for potential colorectal malignancy.

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Among 2,210 average-risk adults screened by colonoscopy, 27.9% had neoplastic lesions and 11 had invasive cancers. Advanced proximal neoplasms were found in 1.3% of patients who had no distal adenomas at all, and 39% of advanced proximal lesions occurred without any associated distal polyp. These findings demonstrate that significant colorectal pathology can exist silently in the proximal colon, reinforcing the importance of investigating any visible warning signs such as rectal bleeding that may prompt diagnostic evaluation.

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CDC clinical guideline (Publication #22-1381, revised February 2023) highlights that colorectal cancer is the 2nd leading cause of cancer death in the U.S. among cancers affecting both men and women. The guideline emphasizes that routine screening saves lives by catching cancer early. Blood in stool is a recognized cardinal symptom of colorectal cancer that patients can self-observe and should prompt timely medical consultation. Several screening modalities recommended in clinical guidelines, including fecal immunochemical tests (FIT) and guaiac-based fecal occult blood tests (gFOBT), are specifically designed to detect blood in stool, underscoring its clinical significance as a warning sign.

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In the NHS cohort of 77,439 women followed from 1988-2012 with 1,527 colorectal cancer cases, 15+ years of rotating night shift work was associated with a 60% increased risk of rectal cancer specifically (HR 1.60, 95% CI: 1.09-2.34, P=0.02). This statistically significant finding was site-specific, as overall colorectal cancer risk was not significantly elevated (HR 1.15, 95% CI: 0.95-1.39, P=0.14 for 15+ years in NHS). The duration-dependent increase in rectal cancer risk suggests cumulative circadian disruption plays a role in rectal carcinogenesis.

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