Hidden Blood in Stool May Indicate Higher All-Cause Death Risk

“Invisible” blood in stool may predict death from a wide range of causes, not just colorectal cancer, according to a study published July 16 in Gut. A positive fecal occult blood test (FOBT) increases all-cause mortality risk, including circulatory, respiratory, neuropsychological, and non-colorectal cancers, by 58 percent.

Testing for the presence of hemoglobin in stool is a widely used tool for colorectal cancer screening, including in the population-based colorectal cancer screening program in Scotland, the Scottish Bowel Screening Programme, that uses mailed test kits for a guaiac FOBT (Immunostics; Ocean, New Jersey, USA).

The researchers analyzed results for all individuals who participated in gFOBT screening in Tayside, Scotland through either a pilot period (March 2000 to September 2007) or the subsequent full program implementation (2007 onwards). Patients were between the ages of 50 and 69 years for the pilot, and up to 74 years during the full program. Test result (positive or negative) were linked with mortality data from the National Records of Scotland database, with follow-up through March 2016.

Based upon the 133,921 patients included in the analysis, positive test results were seen in 2.0 percent of the cohort. As would be expected, those with a positive gFOBT test result had higher mortality. But these results extended beyond colorectal cancer and were seen for all-cause mortality, including circulatory disease, respiratory disease, digestive diseases (excluding colorectal cancer), neuropsychological disease, blood and endocrine disease, and non-colorectal cancers. These findings remained even when adjusting for gender, age, socioeconomic status, and medications, like aspirin, that can cause bleeding.

“It would appear that the association between hemoglobin in feces and premature non-colorectal cancer death cannot be explained simply by its association with obvious confounding factors,” write the authors led by Gillian Libby, from Ninewells Hospital in Scotland. With further validation, the authors suggest “a positive test result could be used alert invitees to the risk of reversible non-communicable disease regardless of the presence or absence of colorectal neoplasia.”

The authors caution that since gFOBT are qualitative tests the effect of an incremental increase in fecal hemoglobin concentration could not pinpointed. However, they explain that gFBOT usually become positive at a concentration of around 80 µg hemoglobin/gram feces, which would be the “high end” of the fecal hemoglobin spectrum that would be expected in a population.

“If the eye is the window to the soul, is a fecal test the window to general health?” asks Uri Ladabaum, from Stanford University in California, an accompanying commentary. “Perhaps more importantly, if occult blood in feces is a predictor of life expectancy and multiple [non-bowel cancer] causes of death, the inevitable next questions concern the implications for organized [bowel cancer] screening programs or opportunistic [bowel cancer] screening.”

Takeaway: Positive FOBT tests may indicate a health risk beyond colorectal cancer.