• colorectal cancer screening
• epidemiology
• health service research

After decades of research, testing for occult blood in faeces is firmly established as a method to screen for colorectal cancer (CRC). Such testing is based on the relatively simple premise that asymptomatic CRCs, and some CRC precursors, may lose small amounts of blood into faeces. The provocative study by Libby et al in Gut,1 which reports the associations between a positive guaiac faecal occult blood test (gFOBT) result and all-cause as well as non-CRC mortality in the National Health Service Tayside Board area of Scotland, suggests that occult blood in faeces may be telling us more than we might have thought. If the eye is the window to the soul, is a faecal test the window to general health?

The current study confirms and expands on the observations of Chen et al, who reported a gradient relationship between all-cause mortality and faecal haemoglobin (f-Hb) concentration in population-based screening programmes in Keelung and Tainan, Taiwan.2 Chen et al and Libby et al found associations between occult blood in faeces and CRC mortality, which is not surprising. However, in the study by Chen et al, with median follow-up of 3.5 years and longest follow-up of 8 years, the adjusted HRs for all-cause mortality ranged from 1.15 (95% CI 1.07 to 1.24) to 1.67 (95% CI 1.54 to 2.07) for persons with f-Hb concentrations of 20–49 and ≥450 ng Hb/mL, respectively (trend test p<0.0001), compared with the reference group of 1–19 ng Hb/mL (whose risk did not differ from that of persons with undetectable f-Hb). …