Two cheap blood tests could help multiple sclerosis patients work out if they are at risk of having a relapse within months.
A blood test could reveal MS risk
The information could help doctors prescribe the right drugs to stop this happening.
Many multiple sclerosis patients, particularly in the early stages of the disease, do not suffer constant symptoms.
Attacks of the disease, called "relapses", can bring nerve-related symptoms such as fatigue, poor coordination and paralysis.
However most patients find that, at first, these symptoms can disappear, with a gap of months or even years before they come back.
This presents problems for doctors, who are trying to give the patient a firm diagnosis, and an idea of what to expect.
The tests, which look for signs of an immune reaction to particular proteins, may help.
A team of researchers from Austria tested patients who had suffered what they believed to be their first attack of MS symptoms.
Their blood was tested once the symptoms had disappeared.
Those who had the antibodies - signs that the immune system has been activated against these proteins - were much more likely to suffer a second attack within months.
In all, 95% of those who had the antibodies experienced a relapse, usually within eight months.
In contrast, among those who tested negative, only a quarter had suffered a relapse, even years later.
Even these relapsed patients on average took four years to have a second attack.
There are no cures for multiple sclerosis, even if the disease is caught early, but there are treatments which studies suggest can increase the period of time in between relapses.
A positive blood test could mean that the patient is a good candidate for these drugs, whereas someone who has a negative result could stay off the drugs and avoid the side effects involved.
Stephen Reingold, from the National Multiple Sclerosis Society, said: "You may end up with a benefit there - at least a short-term benefit.
"But we don't know if treatment at that stage will make any difference 15 or 20 years from now."
The study was published in the New England Journal of Medicine.