SCIENTISTS are conducting the world’s first clinical trials on humans to convert blood from one group to another in a breakthrough that could help combat shortages of donors.

They have discovered bacterial enzymes that can be used to convert blood types A, B and AB into the much sought-after O negative type.

The O group is in high demand because it can be given to anyone of any blood group in a transfusion. It would ease blood shortages in hospitals and reduce the risk of patients being given the wrong type of blood, which can be fatal.

The technique uses enzymes from two bacteria that are able to remove the sugar molecules, which dictate the group to which the patient belongs, from the surface of blood cells.

Professor Henrik Clausen of the centre for glycomics at Copenhagen University made the discovery after looking at more than 2,500 fungi and bacteria.

The technology is being tested by ZymeQuest, a company in Beverly, Massachusetts. It hopes to make it available widely and inexpensively by 2009.

“The trials are going well,” said Clausen. “We had a hypothesis that the enzyme we needed was likely to be found in the gut, and it turned out to be right.”

The technique has been welcomed by experts. Geoff Daniels, senior research fellow at the Bristol Institute for Transfusion Sciences said: “The theory is that you would be able to convert large quantities of group A and B blood easily.

“In the shorter term, it will be beneficial for patients with problems like sickle-cell anaemia and thalassaemia [a severe form of anaemia]. This group needs regular transfusions but it can be difficult to organise the blood donations for them.”

There are still obstacles to be overcome, however, before all blood can be made usable in any patient. Each blood group is further subdivided into two types, rhesus positive (which circulates in 83% of the population) and rhesus negative.

People who have positive blood can safely receive negative transfusions but the reverse carries risks.

“People are trying to find a way of turning rhesus positive into rhesus negative,” said Clausen. “But rhesus is a protein and it is a lot more complicated. It would be a long way off.”

He added: “Mixing the rhesus groups isn’t ideal, but it is not usually catastrophic. It is mixing the A B O types that causes real problems.”

About 42% of British people have type A blood, 10% type B and 4% type AB. The rest have type O.

A spokesman for the National Blood Service said: “We welcome any medical development or research that is likely to be beneficial to patients in the future.

“The service requires about 8,000 voluntary donations daily in order to meet hospital demand. The demand for blood never stops.”

Between 1996 and 2003 five patients died after being given the wrong blood type. The problem also contributed to a further seven deaths and caused serious illness in 49 patients.

The system of blood transfusions can be wasteful, with one in 10 samples never used. Each unit of two-thirds of a pint of blood costs £120 to store and is unusable after 35 days.

The unreliability of donations means the National Health Service can be vulnerable to occasional shortages, particularly at peak periods.

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