A new procedure for testing for cancer of the colon is worse than the standard test it would have replaced, researchers have discovered.

Hydrocolonic ultrasonography, an ultrasound technique using water in the colon, was unable to detect any cancers and only one polyp in a group of 52 patients, 26 of whom had polyps, three had cancer and polyps and one had cancer alone.

Ultrasonography also detected cancers and polyps which were, in fact, not there.

Patients in the study group also found ultrasonography to be uncomfortable. Six had to stop the test, and there were also two complications.

The study, carried out by the University of California and led by Dr David Chui, said that the usefulness of the new technique was "limited", and that the standard colonoscopy was more reliable and accurate. The technique was particularly ineffective with obese patients, again making it of limited benefit to the consultant.

Ultrasonography had been seen as a better alternative to colonoscopy because it was cheaper to perform, less invasive and did not require the patient to be sedated (NEJM, December 22, 1994).

Liver biopsies can be risky, and can kill about 0.1 per cent of patients, usually because the gall bladder is punctured. The new technique, where the need le is guided by ultrasonography, should be safer. Many consultants now believe that standard biopsies can no longer be defended.

But, say two specialists at Lincoln County Hospital, this is not always the case. Writing in the BMJ, they point out that serious bleeding occurred in 2.5 per cent of guided biopsies, against 1.6 per cent of those where the physician "felt" the needle in. Pain was experienced by 25 per cent of patients who had non guided biopsies, and almost as many 22 per cent suffered pain when the needle was guided by ultrasonography.

To arrive at a definitive answer, they suggest a national reporting scheme for assessing the two techniques.