A simple blood test could help tailor treatment for suffers of rheumatoid arthritis (RA).
Studies show 80% of patients suffering from the condition are believed to have one of two antibodies that usually signify they are more likely to respond to an advanced form of treatment.
Trials of a biologic drug, rituximab, also known as MabThera, show that eight out of 10 patients have a good chance of being helped by the treatment, which targets the immune system.
For the 20% of patients who do not have one of the antibodies, it is unlikely to be worthwhile using the drug and this could stop health trusts wasting money on unproductive treatments.
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."