Scientists on Monday unveiled a quick, cheap way to detect sepsis, a life-threatening condition in which the body is attacked by its own immune system.

In clinical trials at Massachusetts General Hospital in Boston, the researchers -- analysing a single drop of blood with a thumb-size filtering device -- singled out sepsis patients in a matter of hours with 95 percent accuracy.

Currently, nearly a third of sepsis patients are misdiagnosed with devices that can take days to yield results.

For every hour that a sepsis diagnosis is delayed, the risk of death increases by nearly eight percent, previous research has shown.

"We believe that this approach may allow us to identify patients at risk of developing sepsis earlier than any other method," said Jarone Lee, director of an intensive care unit at Massachusetts General and co-author of a study in Nature Biomedical Engineering.

Sepsis occurs when the body's immune system runs amok in reaction to a major infection, leading to low temperature, vomiting and -- in extreme cases -- tissue damage, organ failure and death.

The condition affects at least 30 million people worldwide every year, and leaves five million dead, according to a recent study in the American Journal of Respiratory and Critical Care Medicine.

Up to half of people who survive severe sepsis suffer from post-traumatic stress disorder, chronic pain, organ dysfunction or amputations, according to the Sepsis Alliance, a charitable advocacy organisation in the United States.

The test devised by the researchers isolates a specific type of white blood cell, called a neutrophil.

In earlier research, senior author Daniel Irimia, a surgeon at the hospital and assistant professor at Harvard Medical School, noticed that spontaneous movements of these white blood cells corresponded to the likelihood that patients would develop sepsis.

Irimia and colleagues developed a small, hand-held device that coaxes neutrophils through a microscopic maze.

"The striking performance" of the device "brings into focus the fundamental role that neutrophils play during sepsis," Irimia said in a statement.

Follow-up tests with a larger and more diverse group of volunteers are underway.