Visible blood in urine is the best known indicator of bladder cancer but new research  finds that invisible blood in urine may be an early warning sign of bladder cancer. 

Scientists at the University of Exeter Medical School found that 1 in 60 people over the age of 60 who had invisible blood in their urine transpired to have bladder cancer. Thay's about half those who had visible blood in their urine but higher than figures for other potential symptoms of bladder cancer that warrant further investigation. 

The study examined more than 26,000 people whose anonymised data contributed to the Clinical Practice Research Datalink; this is a large research database used by the Exeter team in several cancer studies. The team found that the risk of bladder cancer was 1.6 per cent in people over 60 who had invisible blood in their urine.

Around 10,000 people in the UK are diagnosed with bladder cancer each year. The condition is more common in men than women and in older people, with the average age of diagnosis at 68.

Lead author Sarah Price, a PhD student at the University of Exeter Medical School, led the study. "It is well known that if you see blood in your urine you should contact your GP, who is likely to refer you for tests. But there is no clear guidance for GPs on what to do if they detect blood that is not visible during routine tests. We are hopeful that our findings will now lead to robust guidance that it warrants further investigation. Early diagnosis is crucial to have the best chance of successfully treating bladder cancer.

"The three-quarters of patients who are diagnosed early have much better outcomes than those whose disease is diagnosed late. Anything we can do to boost early detection is crucial to help save lives." 

Published in the British Journal of General Practice.