Unseen stool blood is linked to a heightened risk of death from all causes, as well as from bowel cancer, according to Scottish researchers.
They said it was particularly associated with a heightened risk of dying from circulatory, respiratory, digestive, blood, hormone and neuropsychological diseases, and other types of cancer.
“It may reflect the reason why male gender, age and deprivation are such strong risk factors”
Faecal occult blood test, or FOBT for short, is currently used to screen for bowel cancer or its precursor, polyps, in older people, noted the researchers.
Previous studies have indicated that stool blood might predict life expectancy, independent of its association with bowel cancer.
However, potentially influential factors, including drugs that might predispose to internal bleeding – aspirin, for example – were not accounted for.
To try and address this gap, the researchers drew on linked prescribing, bowel cancer screening, and mortality data for nearly 134,000 people in Tayside from March 2000 to the end of March 2016.
In all, 131,207 people, aged between 50 and 74, tested negative for unseen stool blood and 2,714 – just over 2% – tested positive during this period. Their survival was tracked from the date of this first test until death or the end of March 2016, whichever came first.
Older age, increasing levels of deprivation, and male gender were associated with a greater likelihood of a positive test result. Prescriptions for aspirin or other drugs that boost the risk of digestive tract bleeds were also more likely to be associated with a positive test result.
Overall, people who had a positive FOBT result were nearly eight times as likely to die of bowel cancer as those who tested negative, after taking account of gender, age, deprivation, and drug treatment.
But more surprising was that a positive FOBT result was also associated with a 58% heightened risk of death from all causes other than bowel cancer, said the researchers.
”The inevitable next questions concern the implications for organised screening programmes or opportunistic screening”
It was associated with a significantly greater risk of death from circulatory, respiratory, digestive tract, neuropsychological, blood and hormone diseases, as well as other types of cancer.
The researchers highlighted that older age, male gender, and increasing levels of deprivation were themselves risk factors for death from all causes.
Yet, even after adjusting for these factors, a positive FOBT result was still strongly associated with early death, said the researchers in the journal Gut.
“Although increased [unseen stool blood] cannot be a cause of death, it may reflect the reason why male gender, age and deprivation are such strong risk factors,” they suggested.
They highlighted, however, that their study was observational and could not establish a cause, and there were no obvious explanations for their findings.
They speculated that generalised inflammation, manifest in gut inflammation and bleeding, may provide the missing link.
For example, they highlighted that there was good evidence that most solid cancers and Alzheimer’s disease developed against a background of inflammation.
The researchers suggested that a positive FOBT result might be used to alert bowel cancer screening programme participants who do not have the disease to the possibility they might be at risk of other illness, and the need for a healthier lifestyle or drug treatment.
In a linked commentary in the same journal, Professor Uri Ladabaum, from Stanford University School of Medicine in the US, said hidden stool blood “may be telling us more than we might have thought”.
“If occult blood in faeces is a predictor of life expectancy and multiple [non-bowel cancer] causes of death, the inevitable next questions concern the implications for organised [bowel cancer] screening programmes or opportunistic screening,” he said.