I am red-green colour blind and I’m well aware of my general inability to distinguish red particularly well. In particular, I often miss subtler shades of pink. Apart from a tendency to wear inappropriate shirt and tie combinations it’s hardly life threatening. Or so I thought.
However, it is perhaps rather more than an inconvenience that blood is red. People that are colour-blind may be unable to spot early signs of blood loss. And as any fule kno unexpected blood rings big fat alarm bells for the Big C.
A good example is blood in the urine. I doubt I would miss frank gross haematuria but a red-green colour deficiency makes it easy to miss an elegant pink tinge in my urine. This simple study from some urologists in Preston took 200 male patients with bladder cancer and assessed them for colour deficiency using an Ishihara plate test. They found 21 blokes (10.5%) had red-green or ‘complete colour blindness’. The presentation at diagnosis was frank haematuria in 74% of the non-colour blind versus 62% of the colour blind (non-significant).
The study also looked at the histology and the non-colour blind had 69% with superficial disease and the rest had invasive bladder cancer. The colour-blind group had 42% with superficial disease and 58% with less favourable histology. This is statistically significant (p<0.01).
There is sound logic to back up these findings. Colour-blind men can’t pick up some of the early signs of disease when it involves spotting colour changes in bodily fluids. So they are presenting later with more advanced disease. Not good. However, this is a small study – only having 21 cases of bladder cancer in colour-blind men limits how far I would want to rely on the findings.
Colour-blindness is treated as nothing more than an evolutionary oddity; good for teaching the basics of X-linked inheritance but of no clinical significance. Yet, it might have a little more impact than you think.
Reference: Katmawi-Sabbagh, S., Haq, A., Jain, S., Subhas, G., & Turnham, H. (2009). Impact of Colour Blindness on Recognition of Haematuria in Bladder Cancer Patients Urologia Internationalis, 83 (3), 289-290 DOI: 10.1159/000241669