What’s it for?
Barium enemas are given to test for a range of disorders of the lower intestinal tract, including cancer, diverticulitis, polyps, irritable colon, ulcerative colitis and Crohn’s disease. Doctors may recommend a barium enema if you have chronic diarrhoea or constipation, blood in the stools or unexplained weight loss.

What does it involve?
The basic technique is to X-ray the lower colon. As the soft tissues in that area look similar in an X-ray, a liquid containing radiopaque barium sulphate is introduced into the colon via an anal enema. To maximise the reach of the barium liquid, the patient’s colon must be as empty as possible, so fasting and laxatives are prescribed for two days before the test.

The test itself has the patient lying on a X-ray table while the radiographer looks at a real-time X-ray (fluoroscope) of the colon, now clearly revealed by the barium liquid. Air is sometimes pumped into the colon along with the barium to improve the quality of the images (double-contrast technique).

The whole procedure takes about half an hour, during which you may be asked to shift position and hold your breath for still pictures to be taken. It is said to be not painful, but you will almost certainly feel bloating, cramping and possibly colonic muscle spasm. These can be partially relieved if peppermint oil is added to the barium liquid (Br J Radiol, 1995; 68: 841-3).

How accurate is the test?
Studies show that it’s about 80-90 per cent accurate in diagnosing colon cancer (Radiology, 1999; 211: 211-4), but it cannot detect tumours smaller than 1 cm. Other intestinal conditions have about the same rate of detection.

What are its dangers?
Barium may remain in the colon and harden, causing severe constipation. It can also produce so-called barium granulomas, where the colon wall is inflamed in reaction to the barium. More serious is perforation of the bowel. Under pressure from the barium or air, the colon may split open, spilling its contents into the abdomen. Those with a colon weakened by inflammatory bowel disease, ulcerative colitis, diverticulitis or Crohn’s are particularly at risk.

With the procedure, the radiation dose is relatively high compared with other tests. Radiologists try to play down the risks, pointing out that the radiation dose is equivalent to 16 months’ worth of normal background radiation. Nevertheless, they do acknowledge that the dose should ideally be reduced (Br J Radiol, 2002; 75: 652-6).