ABSTRACT
The incidence of colorectal cancer continues to increase worldwide, and although the prognosis has improved, survival for five years after diagnosis remains less than 50% overall. The most important prognostic factor in colorectal cancer is the stage at diagnosis. Screening, which takes its name from the practice of using screens to sift gravel from river beds to find nuggets of gold, involves the testing of asymptomatic people with a view to diagnosing disease in its early stages so that the outcome of treatment is improved. With cancer screening, if this can include the detection of pre-malignant disease, the screening process may impact on the incidence of the disease as well as its attendant mortality. For many years, the approach to detecting blood in faeces relied on the indirect guaiac test. In order for haemoglobin to be detected, it has to be exposed by lysis of the red cells.
