Narrator: This is Science Today. Each year, between 250 and 300 thousand Americans are diagnosed with mini-strokes that are called transient ischemic attacks, or TIAs. And there may be many more of equal number that occur, but are never diagnosed. Dr. S. Claiborne Johnston, a neurologist at the University of California , San Francisco says TIA patients are at high risk of suffering a major stroke within the first few days to weeks after an attack.

Johnston : We've only just begun to appreciate this high overall risk of stroke in the TIA population and so it was mostly clinical judgment about who was at high risk and who not.

Narrator: Johnston devised a simple prognostic scoring system for physicians that can improve the prediction of stroke risk in these patients.

Johnston : Basically, what we came up with was a tool that lets emergency physicians, neurologists, primary care docs, figure out whether a person's risk for having a stroke after a TIA is high or low. That's one of the advantages of the score, is that we can take those highest risk patients and put them in a hospital where we can watch them very carefully.

Narrator: For Science Today, I'm Larissa Branin.