Routine blood tests could contain unexpected clues about the likelihood of colorectal cancer among adults younger than 45, according to new research examining commonly measured liver enzymes.
An analysis by Epic Research found that adults under 45 with lower levels of two liver enzymes — aspartate transaminase (AST) and alanine transaminase (ALT) — were more likely to be diagnosed with early-onset colorectal cancer than those with moderately higher levels.
Researchers stressed, however, that the findings show an association rather than proof that low AST or ALT levels cause colorectal cancer. The analysis has also not yet been published in a peer-reviewed journal, and experts say the findings should not change current cancer-screening recommendations.
Lower liver enzyme levels linked to higher likelihood
Researchers examined health records from more than 11,000 Americans between the ages of 18 and 44 who underwent their first colorectal cancer screening between 2017 and 2025. Participants had also received at least one AST or ALT test during the three years before screening.
Adults with AST levels below 14 units per litre had a 65 per cent higher likelihood of receiving an early-onset colorectal cancer diagnosis compared with those whose levels were between 14 and 29.
Similarly, people with ALT levels below 14 had a 68 per cent higher likelihood of being diagnosed compared with those in the 14-to-29 range.
Higher enzyme levels showed the opposite association. AST levels of 30 or above were linked with a 22 per cent lower likelihood of colorectal cancer, while ALT levels of 30 or higher were associated with a 29 per cent lower likelihood.
Researchers also examined changes in liver enzyme levels over time. Rising AST was associated with a 27 per cent lower likelihood of colorectal cancer, while rising ALT was associated with a 26 per cent lower likelihood. Declining levels did not show a significant association with cancer.
Findings should not cause alarm, experts say
Despite the results, medical experts cautioned against interpreting low AST or ALT levels as evidence that someone has or will develop colorectal cancer.
The enzyme levels categorized as low in the analysis could still fall within ranges generally considered clinically normal. Researchers also emphasized that people should not attempt to deliberately increase their AST or ALT levels.
Low enzyme levels could instead reflect other aspects of a person’s health, including muscle mass, frailty or nutritional factors. Researchers say further studies are needed to determine whether these factors could help explain the observed association.
Other routine laboratory measurements, including triglycerides, cholesterol and potassium, were also examined, but researchers found no association between those markers and early-onset colorectal cancer.
Colorectal cancer rising among younger adults
The findings come amid growing concern over increasing rates of colorectal cancer among younger people. In the United States, colorectal cancer has become the leading cause of cancer death among people under 50.
Scientists are still trying to understand what is driving the trend. Potential factors under investigation include genetics and family history, obesity and metabolic health, diet, physical inactivity, the gut microbiome, antibiotic exposure and delays in recognizing symptoms among younger patients.
However, experts say none of these factors fully explains the increase.
Screening recommendations remain unchanged
The new findings do not alter current colorectal cancer screening recommendations.
In the United States, adults at average risk are generally advised to begin colorectal cancer screening at age 45. People with symptoms, a family history of the disease or other risk factors may be advised to begin screening earlier.
Blood-based screening has also become an option for some adults. The American Cancer Society recently added blood-based tests to its recommended screening choices for average-risk adults aged 45 and older who have not completed or have declined stool-based tests or visual examinations.
However, colonoscopy remains the gold standard, and a positive blood-based screening result requires follow-up with a colonoscopy.
Researchers say the latest findings should primarily serve as a starting point for further investigation rather than a reason to change medical practice.
For now, experts recommend following established screening guidelines and discussing symptoms, family history and individual risk factors with a health-care provider rather than relying on AST or ALT levels alone.
