LOS ANGELES _ Most doctors are uncertain about approaches to finding the cause of mysterious and life-threatening events called “cryptogenic strokes,” and about half of healthcare providers say they don’t know enough about them, according to a report released Wednesday.

A stroke is usually caused by a blood clot that blocks the flow of blood to the brain. But sometimes, despite testing, a stroke’s cause is “cryptogenic,” or unknown. An estimated 30 percent of ischemic strokes in the U.S., about 200,000, are considered cryptogenic.

Finding the cause is important because a prior stroke is the No. 1 one risk factor for a second stroke, which is 16 times more likely to be fatal. Stroke is the No. 2 cause of death in the world and a leading cause of adult disability, according to the American Stroke Association, which released the report.

“The ability to discern the causes of cryptogenic strokes has profound implications for preventing secondary strokes and improving patient outcomes,” said Mary Ann Bauman, M.D., chair of the American Stroke Association Advisory Committee.

Yet up to 70 percent of doctors surveyed said they’re uncertain about the best approaches to determine a cryptogenic stroke’s cause.

A survey was conducted in an effort to increase awareness and support for better diagnostic tools, interventions and a systematic approach to managing these patients, the American Stroke Association said. The survey polled 652 healthcare professionals, including neurologists, cardiologists, primary care physicians and stroke coordinators.

Survey results were discussed by a healthcare experts at the first cryptogenic stroke conference, in October. Baumann said she hopes the conference report helps educate doctors and the scientific community, but notes that more studies are needed on cryptogenic stroke.

Atrial fibrillation, or AFib, is a quivering or irregular heartbeat that increases the risk of a cryptogenic stroke five times. Healthcare professionals recognize that AFib can cause a cryptogenic stroke, they’re not always sure how best to detect the disorder, according to the survey. But AFib can go undetected because it often has no symptoms and may occur infrequently.

Disparities in stroke care can also lead to obstacles in treatment and diagnosis. Compared with whites, African-Americans have twice as high a risk of first stroke as well as of stroke death.

The report was released during the International Stroke Conference in Los Angeles, where almost 5,000 experts around the world met to discuss the latest stroke science.