A large electronic health record study suggests that difficulty recognizing painless blood in urine may delay diagnosis and worsen long-term survival for bladder cancer patients with color vision deficiency, highlighting overlooked risks in symptom recognition and screening.
Study: Impact of colour vision deficiency on bladder and colorectal cancer survival. Image credit: SaiArLawKa2/Shutterstock.com
Bladder cancer patients who are unable to detect blood in the urine due to color vision deficiency may have poorer survival outcomes, specifically in bladder cancer, than those without the deficiency, according to a large retrospective analysis that the authors describe as hypothesis-generating, reported by a new study published in Nature Health.
Missed visual warning signs can delay cancer diagnosis
Colorectal cancer is the third most common cancer among men and women, and urinary bladder cancer is the fourth most common cancer among men in the United States. These two malignancies are associated with high mortality rates.
Presence of blood in urine and stool is often the first sign of bladder and colorectal cancers, respectively. Early detection of this sign by the patient is a vital indicator for seeking medical attention on time.
However, patients with color vision deficiency are at higher risk of delayed disease diagnosis because they are unable to detect red in urine or stool. This is particularly relevant in the case of painless hematuria, where blood appears in the urine without causing pain. In such cases, patients have to rely on identifying blood in their urine as an indication to seek medical attention.
Existing evidence indicates that patients with color vision deficiency and bladder or colorectal cancer may delay care-seeking due to a lack of recognition of the blood, which may subsequently increase the risk of being diagnosed with more advanced or invasive disease, as cancer cells may have additional time to progress before detection because of the delayed care-seeking.
Given the potential impact of color vision deficiency on cancer diagnosis, researchers from Columbia University, Stanford University School of Medicine, and Beaumont Health, USA, conducted a study to explore whether color vision deficiency is associated with worse cancer outcomes.
Matched analysis of cancer patients with visual deficiency
The researchers analyzed electronic health records data from health organizations in the United States and international sites to evaluate the differences in survival rates between bladder cancer and colorectal cancer patients with and without color vision deficiency.
A total of 135 bladder cancer patients and 187 colorectal cancer patients with color vision deficiency were compared with matched patients without the deficiency.
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The study analysis revealed that patients with both bladder cancer and color vision deficiency have shorter overall survival than the matched patients without color vision deficiency.
The mortality analysis indicated that the patient group with color vision deficiency exhibits a 52% higher risk of death over 20 years compared to the group without color vision deficiency, with a risk ratio of 1.52.
In colorectal cancer, however, no significant difference in survival probability was observed between patients with and without color vision deficiency.
Symptom reliance and screening gaps shape survival differences
The study identifies color vision deficiency as a potentially important but under-recognized risk factor for reduced survival probability and higher mortality risk in patients with bladder cancer. However, no such risk has been identified in patients with colorectal cancer. The authors emphasize that the findings are associative rather than causal and should be interpreted cautiously, particularly given limitations in available clinical detail.
Worse survival outcomes observed in bladder cancer patients with color vision deficiency may be attributed to delayed recognition of painless hematuria, which often leads to cancer diagnosis at more advanced stages. Although these risk factors should be equally applicable to colorectal cancer patients with color vision deficiency, the study did not detect similar outcomes in this group of patients, which the authors note may reflect limited statistical power rather than a true absence of effect.
Various factors can explain this discrepancy. In approximately 80–90% of bladder cancer cases, the only initial symptom is painless hematuria, meaning that the patient’s ability to identify blood in the urine is the sole indicator to seek medical attention.
Colorectal cancer at an early stage, on the other hand, may present with a variety of other symptoms, including abdominal pain, change in stool habit, rectal bleeding, and weight loss. These symptoms may indicate disease even in patients who cannot see blood in the stool.
Screening is another vital factor that may explain the observed differences between bladder and colorectal cancer patients. In the United States, public health authorities recommend screening for colorectal cancer in adults aged 45 years and above. However, no such recommendation exists for asymptomatic bladder cancer screening, further increasing the possibility of underdiagnosis, especially in vulnerable populations like patients with color vision deficiency.
In the United States, color vision screening is not routinely performed. Only a limited number of states require screening during childhood, and most adults with color vision deficiency remain unaware of their condition, particularly when symptoms are mild and do not interfere with daily activities.
These factors may increase the likelihood of including patients with undiagnosed color vision deficiency in the study groups, potentially biasing the observed associations toward underestimating the true effect. In addition, the authors note that cancer staging data were sparse in the underlying records, limiting direct assessment of disease stage at diagnosis.
Overall, these findings provide a foundation for future research into whether screening for bladder cancer should be introduced for high-risk individuals with color vision deficiency to improve survival, as well as for increased clinical awareness of visual limitations that may affect symptom recognition.
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