A blood test could reveal when a flare-up of rheumatoid arthritis is likely to occur, new research suggests.

Scientists say a never-before-seen cell type could forewarn of rheumatoid arthritis symptoms.

The presence of the cell dramatically increases in the bloodstream in the week leading up to a flare-up, a study published in the New England Journal of Medicine suggests.

Researchers say the cells could be used as a warning for oncoming pain and discomfort.

For doctors and patients, intervention before a flare-up is always better than just treating symptoms

Dr Robert Darnell, a Howard Hughes Medical Institute investigator at the Rockefeller University, said: “If we can reliably identify these new cells in patients, we may be able to tell them ‘You’re about to have a flare,’ so they can prepare themselves.

“This would make flares less disruptive and easier to manage.”

The study suggests the newly discovered cells may hold a key to understanding the root causes of rheumatoid arthritis – perhaps offering a way to prevent the flares from taking place at all.

Rheumatoid arthritis is a disease of the immune system that causes inflammation in the joints, especially around the hands and feet.

It can be debilitating and frequently strikes people in their 30s or 40s.

The symptoms come in waves, with stretches of relative quiet interspersed with painful flares. There is currently no cure.

Over a period of four years, patients posted their blood samples to the lab and reported their symptoms, noting when flares occurred.

Researchers then analysed blood collected the weeks before symptoms worsened.

About two weeks before a flare, scientists saw increased activity from B cells, which create antibodies.

But in the samples collected a week later, in the days just prior to a flare, they noticed a signature for a cell that did not match any known cell type.

The cells were normally present in low levels in the blood, then spiked in the week before a flare, and all but disappeared during the flare itself.

They named their new discovery PRIME cells.

Dana Orange, assistant professor of clinical investigation and a co-author on the paper, said: “We were so surprised to see that the genes expressed right before a flare are normally active in the bone, muscle, and extracellular matrix – strange pathways to find in blood cells.

“That really piqued our interest.”

Dr Darnell concluded: “For doctors and patients, intervention before a flare-up is always better than just treating symptoms.

“If these cells are the antecedents to joint sickness, they become a potential target for new drugs.”

The researchers say the next step is to test in more patients whether the presence of these cells can predict a flare-up.