A simple test that can detect sepsis from a single drop of blood is reported in a paper published online this week in Nature Biomedical Engineering. The test is quick, cheap and accurate, and could be easily adapted to monitor patients at risk of sepsis.

Sepsis - a life-threatening condition in which the body’s extreme response to severe infection damages tissues and organs - is misdiagnosed in approximately 30% of patients. This is because current tests have poor specificity and are slow - taking days to provide results, which leads to unnecessary antibiotic prescriptions, thus promoting the spread of antibiotic-resistant strains of bacteria.

Daniel Irimia and colleagues designed a device in which a drop of blood fills a maze of microscopic channels. A machine-learning algorithm then correlates the movement of neutrophils - the immune system’s ‘first responders’ - in the maze with sepsis severity to calculate a ‘sepsis score’. The researchers show that the test runs in only a few hours and that in a double-blind observational study of 42 patients the sepsis score differentiated healthy individuals from those with sepsis with over 95% sensitivity and specificity.

Although the test needs to be validated using a larger and more diverse set of patients, it has the potential to increase the survival rates of patients at high risk of sepsis and to reduce antibiotic overuse.