Seeing blood in your urine is often the first clue that something is wrong. Many people notice this symptom and seek medical attention, which may lead to an early diagnosis of bladder cancer. However, for people with color blindness, detecting that warning sign can be much more difficult. Many people with color blindness have trouble seeing the color red, so blood in the urine may go unnoticed.
Researchers at Stanford Medicine and collaborating institutions report that ignoring this early symptom can have serious consequences. After analyzing health records, the researchers found that people with both bladder cancer and color blindness had a 52% higher chance of dying over a 20-year period compared to bladder cancer patients with normal vision.
Researchers believe that colorblind people may be unable to recognize blood in their urine, which may delay them receiving treatment. As a result, the disease may be diagnosed at a later stage when treatment is more difficult and survival rates are lower.
“We hope this study raises awareness not only of patients with color blindness, but also of our colleagues who care for these patients,” said Ethan Rahimy, MD, adjunct clinical associate professor of ophthalmology and senior author of the study published in 2006. natural health.
The study’s lead author is Mustafa Fattah, a medical student at Columbia University Vagelos College of Physicians and Surgeons.
Color blindness and cancer risk
Color blindness, also known as color blindness, is more common than many people realize. It affects approximately 1 in 12 men and 1 in 200 women. The most popular type prevents the differentiation of red and green shades. This can create everyday challenges such as interpreting signals, coordinating clothing, and determining whether meat is fully cooked.
Bladder cancer is also very common in men, who develop the disease about four times as often as women. In 2025, approximately 85,000 Americans are expected to be diagnosed with bladder cancer.
Previous reports and small studies had already suggested that color blindness may delay the diagnosis of certain diseases. If blood in stool or urine cannot be easily recognized, diseases such as colorectal cancer or bladder cancer may be discovered later. A 2009 study of 200 men with bladder cancer found that those with color blindness were more often diagnosed at a more advanced and invasive stage than those with typical vision.
Another experiment conducted in 2001 asked participants to identify which images of saliva, urine, or stool contained blood. People with normal vision correctly identified the samples 99% of the time, while color-blind participants only did so 70% of the time.
These early findings led Rahimy and colleagues to investigate whether color blindness ultimately affects survival in people diagnosed with bladder or colorectal cancer.
Search millions of health records
To investigate this question, the researchers used a large-scale research platform called TriNetX. The system compiles real-time electronic medical records from around the world and includes approximately 275 million identified patient records.
The database is so large that scientists can use diagnosis codes to identify groups of patients who share unusual combinations of symptoms.
“The power of this kind of research is that you can cherry-pick a specific target population, in this case color-blind patients who have developed bladder cancer or colorectal cancer,” Rahimy said. “Such combinations are rare, but when you cast your net over the ocean’s worth of data, you have a better chance of catching rare fish.”
Researchers identified 135 people diagnosed with both color blindness and bladder cancer, along with 187 patients with both color blindness and bladder cancer, from nearly 100 million U.S. patient records.
For each group, the researchers created a comparable control group of patients with the same cancer diagnosis, similar demographic and health characteristics, and normal vision.
Among bladder cancer patients, those with color blindness were less likely to survive than those with normal vision. Over 20 years, the overall risk of death was 52% higher in the colorblind group. (Death risk includes death from any cause.)
“That was our working hypothesis based on previous research,” Rahimy said.
Why colorectal cancer showed a different pattern
The researchers expected to observe a similar pattern among patients with colorectal cancer. Instead, no statistically significant difference in survival was found between patients with and without color blindness.
One reason may be that colorectal cancer usually presents with some early symptoms. “Blood in the stool is not the main symptom or the most common symptom presented by these patients,” Rahimy said.
Studies show that nearly two-thirds of colorectal cancer patients initially complain of abdominal pain, and more than half notice a change in their bowel habits. In contrast, 80% to 90% of bladder cancer patients initially notice blood in their urine without any pain.
Regular screening also plays an important role. Screening for colorectal cancer is widely recommended for most people between the ages of 45 and 75, reducing the reliance on noticing blood in the stool as the first sign of a problem.
“There is more focus and public awareness on early detection of colorectal cancer than ever before,” Rahimy said.
Why the risk is even higher
The researchers cautioned that the observed difference in mortality rates may actually be an underestimate. The study was based on standard diagnostic codes, called ICD-10 codes, recorded in electronic medical records.
Many people with color blindness are never formally diagnosed and are therefore classified as having normal vision in databases.
“Most people with color blindness usually function normally and have no other vision problems. Many affected people may not even be aware that they have color blindness,” Rahimy said.
Improving patient and physician awareness
This finding indicates that additional research is needed to better understand how color blindness affects disease detection.
“This is a 30,000-foot view. If we see certain trends or things that need further investigation, those deserve their own more detailed analysis and study,” Rahimy said.
The results have already sparked debate among medical experts. Rahimy said urologists and gastroenterologists, including colorblind colleagues, told him they had never considered colorblindness as a factor in cancer diagnosis. Some clinicians said they might start including questions about color blindness in screening questionnaires.
“If this study raises awareness and people read this and casually pass it on, then I think it’s done its job,” Rahimy said.
For people with color blindness, this finding highlights the importance of regular health checkups. Doctors recommend getting a urine test during your annual checkup, and you may want to enlist the help of your partner or family to monitor changes.
“If you’re not sure whether you’re experiencing a change in urine color, it may be worth having your partner or someone you live with regularly test their urine for blood, just to be safe,” Rahimy says.
Researchers at Beaumont Health contributed to this study.
This study was funded by the National Institutes of Health (grant P30-EY026877) and Research to Prevent Blindness, Inc.
