Research conducted by Stanford Medicine has revealed a striking connection between colour vision deficiency and bladder cancer survival rates.
The study, published on January 15 in Nature Health, found that individuals who are colourblind face a 52 per cent higher mortality risk over two decades compared to those with normal vision.
The explanation lies in a seemingly simple observation: blood in urine serves as the primary early indicator of bladder cancer, yet those unable to distinguish red hues frequently miss this crucial warning sign entirely.
“I’m hopeful that this study raises some awareness, not only for patients with colourblindness, but for our colleagues who see these patients,” said Dr Ehsan Rahimy, adjunct clinical associate professor of ophthalmology and the study’s senior author.
One in twelve men and one in 200 women are affected by colour blindness
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Colour vision deficiency is considerably more widespread than many realise, with approximately one-in-twelve men and one-in-200 women affected. The condition most commonly impairs the ability to differentiate between red and green tones.
Bladder cancer disproportionately affects males, occurring roughly four times more frequently in men than women. In 2025, some 85,000 Americans received a bladder cancer diagnosis.
Between 80 and 90 per cent of bladder cancer patients first become aware of their condition through noticing blood in their urine, typically without accompanying pain. This makes the visual detection of discoloured urine absolutely critical for early intervention.
Earlier research from 2001 demonstrated that whilst individuals with normal vision correctly identified blood-containing samples 99 per cent of the time, colourblind participants managed only 70 per cent accuracy.
The research team utilised TriNetX, a platform aggregating approximately 275 million anonymised patient records from across the globe.
From roughly 100 million American health records, investigators identified 135 individuals diagnosed with both colourblindness and bladder cancer.
“The power in this type of study is the ability to curate a particular population of interest,” Dr Rahimy explained.
“It’s unusual to have that combination, but when you’re casting a net in an ocean’s worth of data, you have a better shot at capturing a rare fish.”
Intriguingly, the researchers found no comparable mortality difference among colour blind patients with colorectal cancer.
Dr Rahimy noted that bowel cancer typically presents with additional symptoms such as abdominal discomfort and altered bowel habits, while established screening programmes reduce reliance on visual detection of blood.
The study authors recommend that those with colour vision deficiency request urine tests during every annual health check.
Dr Rahimy also suggested an unconventional but practical measure for those uncertain about detecting changes in their urine.
Few practitioners consider colour vision as a factor in cancer diagnosis
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“If you don’t trust yourself to know that there’s a change in the colour of your urine, it could be worth having a partner or somebody you live with periodically checking it for blood, just to make sure,” he advised.
The findings have already prompted discussion among medical professionals. Dr Rahimy reported that urologists and gastroenterologists, including one colourblind colleague, had never previously considered colour vision as a factor in cancer diagnosis.
Some practitioners indicated they may incorporate questions about colour blindness into their screening questionnaires.
