Increased bladder cancer mortality in colourblind patients is potentially because they cannot see blood in their urine, researchers suggest.

Their study of US health records showed a 52% lower 20-year survival rate in 135 patients with colour vision deficiency (CVD) and bladder cancer compared with matched controls with only bladder cancer after adjusting for comorbidities and baseline characteristics.

Blood in urine is the sentinel sign of bladder cancer for 80-90% of patients who present with painless gross haematuria, the US researchers wrote in Nature Health last week.

“The majority of CVDs impair the ability to distinguish the colour red, leading to the possibility of delayed recognition of malignancy and an increased risk of severe disease among patients with CVD and colorectal cancer or bladder cancer,” they wrote.