Melaena (blood in the faeces)

Blood lost higher up the alimentary canal is partly digested, and appears in the faeces as a black discoloration (melaena). Bright blood is passed in disorders of the rectum and anus. Blood in the faeces may be caused by a number of different conditions. In the first place, irksome but essentially harmless conditions of the anus cause loss of blood; they include haemorrhoids, anal fissure and sometimes anal fistula. Inflammation in this area (rectal inflammation) can also cause loss of blood, as can rectal tumours, both benign (intestinal polyps) and malignant (intestinal cancer). Further symptoms are partly related to the cause. Inflammation causes diarrhoea and mucus production, as well as loss of blood. Malignant tumours alter the pattern of defecation, causing mainly constipation, sometimes alternating with diarrhoea. Fissures and haemorrhoids can¬ęcause constipation because defecation is painful. It is thus necessary that extensive examination should be carried out if blood is passed in the faeces (particularly in the case of older people), to exclude the possibility of a malignant tumour. The anus should be inspected for fissures and haemorrhoids; a tumour low in the rectum can be felt with a