Seeing blood in the urine often alerts you to possible bladder cancer. 80 to 90% of patients with this cancer first notice this symptom, without feeling pain.
But for part of the population, this red signal is not so obvious: people with
color blindnesswho have trouble distinguishing red from yellow, can let this first clue slip away without realizing it.
A team from Stanford Medicine and Columbia University has just shown a link between color blindness and death after
bladder cancer. Published on January 15, 2026 in the journal Nature Healththe study is based on the TriNetX network, which brings together more than 275 million anonymized medical records. The results concern both patients and their doctors.
Color blindness and bladder cancer: excess mortality of 52% observed
The researchers isolated 135 patients with both bladder cancer and color vision deficiency, then compared them to 135 similar patients without color blindness. The two groups were matched on age, sex and several chronic diseases. Over twenty years of follow-up, color blind people had a 52% higher overall mortality risk, or a risk multiplied by 1.52.
© Stanford Medicine
The same approach was applied to colorectal cancer, with 187 colorblind patients and 187 controls. This time, no significant difference in survival was found. For the team, this is primarily hypothesis-generating work, as the size of the groups remains modest and color blindness is often undiagnosed in medical records. And all the more so since, as Professor Ehsan Rahimy, clinical associate professor of ophthalmology and lead author of the study, declares, “Most people with color blindness lead normal lives. They have no other vision problems. Many of them don’t even know they have it.“.
When blood in urine goes unnoticed
In 80 to 90% of symptomatic bladder cancers, the first sign reported is the presence of visible blood in the urine, most often without pain. However, color vision deficiency affects approximately 1 in 12 men and 1 in 200 women, generally in the colors red and green. A 2001 study already showed that normally seeing participants detected blood on photos of urine or stool in 99% of cases, compared to 70% for color blind people.
A study carried out in 2009 on 200 men suffering from bladder cancer also found more invasive forms in color blind patients. For these people, any unusual change in the appearance of urine should be a warning, even if the red color is not obvious. Doctors particularly emphasize:
- Dark brown, “cola” or rust-colored urine;
- The presence of clots or dark filaments;
- Frequent urge to urinate or unexplained burning sensations.
What practical consequences for color blind people and caregivers?
“I am optimistic and I think that this study will help raise a little awareness, not only among color blind patients, but also among our colleagues who take care of them.“, said Ehsan Rahimy, an ophthalmologist and senior author, in a Stanford Medicine article. He recommends that affected people request a urine test during the annual check-up, especially if smoking or other risk factors are present.
The doctor also emphasizes the role of those around him: “If you’re not sure if you can detect a change in the color of your urine, it might be a good idea to ask your partner or someone you live with to check for blood periodically, just to be sure.”, he explained. The authors finally recall that their retrospective analysis, based on diagnostic codes and only 135 color blind cases, must be confirmed by prospective studies before considering targeted screening for bladder cancer in people with color vision disorder.
Without adaptation of prevention and monitoring, this common visual defect could continue to weigh heavily on the survival of certain patients.