Rheumatoid arthritis affects the joints

Researchers from Umea University in Sweden say the test should increase the chances that the condition can be treated successfully.

It is based on detecting antibodies produced by patients before they develop symptoms of the disease.

Rheumatoid arthritis is caused by the body's immune system attacking the cartilage in its own joints.

In many cases the disease - which affects almost 400,000 people in the UK, mostly women - leads to severe pain and crippled joints, predominantly the hands and fingers.

Hereditary factors have been shown to be important in how the disease develops.

Tell-tale signs

The test looks for the presence of antibodies produced by the body in response to the presence of proteins called cyclic citrullinated peptides (CCP) which are thought to be associated with rheumatoid arthritis.

Scientists have discovered that the antibodies appear several years before the onset of the disease.

The new test picks these antibodies up, allowing doctors to diagnose the condition long before it breaks out.

This means that treatment can be introduced even before the patient experiences any symptoms.

The Swedish team say it would be appropriate to screen middle-aged people who have a family history of the condition.

Lead researcher Dr Solbritt Rantapaa Dahlqvist told BBC News Online: "The antibodies occurred in one individual nine years before symptoms of the disease.

"Maybe the disease process is gradual and finally when a threshold is reached the disease breaks through."

Another screening test for rheumatoid arthritis - which looks for substances called rheumatoid factors - is currently available.

However, it carries a risk that some people will test positive for rheumatoid arthritis even when they are perfectly healthy.

The Swedish team say their test is more accurate, and that when used in tandem with the existing test they should prove to be virtually infallible.

Dr Madeleine Devey, of the Arthritis Research Campaign, told BBC News Online: "The disease process in rheumatoid arthritis probably starts many years before symptoms occur.

"Given the importance of treating patients as early as possible before joint damage results, this looks as if it might be a useful way of detecting very early disease and identifying patients that are likely to progress to severe disease.

"This might eventually lead to mass screening although I think we need more independent confirmation before we embark on this."

The research is published in the journal Arthritis & Rheumatism.