A simple blood test could lead to a "new era" of tailored therapy for rheumatoid arthritis.

Research has shown patients with certain immune system antibodies are more likely to respond to an advanced form of treatment. Eighty per cent of patients suffering from rheumatoid arthritis (RA) are believed to have one of the two antibodies.

Trial results presented today show they have a good chance of being helped by the "biologic" drug rituximab, also known as MabThera, which targets the immune system.

However, it may not be worth giving the drug to the 20 per cent of patients who test negative.

Professor John Isaacs, from the University of Newcastle, who led the research, said: "This is an important breakthrough in the treatment of this chronic and debilitating condition, heralding the beginning of an exciting new era for patients, physicians and indeed the entire RA community.

"Conventional practice is based on treating the patient population as a whole, leading to some patients cycling on ineffective treatments before achieving the optimum response.

"By identifying in advance which groups are most likely to respond to, or to have an enhanced response to, drugs like rituximab, we can ensure they are treated early enough to prevent irreversible joint damage and disability. Additionally, this will reduce treatment costs by avoiding the use of ineffective drugs."

RA is a disabling auto-immune disorder in which the immune system attacks the body's own joints. An estimated 690,000 people suffer from the disease in the UK, and 26,000 new cases are diagnosed each year. Care and treatment of people with RA combined with the economic burden of lost employment is believed to cost the UK almost £8bn a year.

The new research, presented today at the British Society of Rheumatology annual meeting in Welwyn Garden City, pooled data from two studies comparing patients who tested positive or negative for the antibodies.

All 670 patients responded poorly to standard treatments with Disease Modifying Anti-Rheumatic Drugs such as methotrexate (MTX).

The results showed that 13.2% of positive-testing patients treated with rituximab plus MTX were in remission and no longer showing symptoms after 48 weeks compared with 5.9% of patients who tested negative.

Positive-testing patients on rituximab were three times more likely to experience significant improvement of symptoms than those lacking either of the antibodies.