Diagnosing cystic fibrosis with wearable devices

A wearable sensor that extracts and analyzes sweat could be a useful device for diagnosing and monitoring diseases.Sam Emaminejad/Stanford School of Medicine

Cystic fibrosis is the most common fatal genetic disease nationwide. It causes the body to produce thick, sticky mucus that clogs the lungs, leads to infection, and blocks the pancreas, which stops digestive enzymes from reaching the intestine where they are required in order to digest food.

Mutations in a single gene, called the Cystic Fibrosis Transmembrane Regulator (CFTR) gene, cause cystic fibrosis. In normal cells, the CFTR protein acts as a channel that allows cells to release chloride and other ions. But in people with cystic fibrosis, this protein is defective and the cells do not release the chloride. The result is an improper salt balance in the cells and thick, sticky mucus. A “sweat test” that measures the amount of salt in sweat is the standard diagnostic test for those with symptoms. A high salt level (over 60 mM chloride) indicates cystic fibrosis. However, this test requires patients to visit a health care professional and get lab tests.

A team led by Drs. Ronald Davis and Carlos Milla at Stanford University School of Medicine developed a wearable device and tested whether it could measure chloride and sodium levels in patients with cystic fibrosis. The work was partially funded by NIH’s National Human Genome Research Institute (NHGRI). Results were published online on April 17, 2017, in the Proceedings of the National Academy of Sciences. 

The device was designed to be flexible so it could be worn on the wrist. It contains a wireless, programmable iontophoresis interface, which is placed on a hydrogel containing molecules that stimulate sweat. The interface periodically applies a gentle electrical current to the gel that drives the sweat-stimulating molecules to the skin’s sweat glands. Electrodes then measure the molecules within the sweat. The data is transmitted wirelessly for analysis.

The team tested the device on three patients with cystic fibrosis and six healthy volunteers. Healthy volunteers had average sodium and chloride levels of 26.7 and 21.2 mM, respectively, after 25 minutes. Cystic fibrosis patients had sodium and chloride levels of 82.3 mM and 95.7mM.

The researchers also looked at whether the device could detect changes in glucose. They measured glucose levels in seven healthy volunteers before and after consuming 30 grams of glucose. They compared the results to those of a commercially available blood glucose monitor. For six out of the seven subjects, consuming the glucose after fasting increased glucose levels in both sweat and blood. The results suggest this device may also be useful for monitoring pre-diabetes and diabetes. However, additional measurements and calibration of the sensors are needed to determine the precise correlation between blood and sweat glucose levels using the device.

“Cystic fibrosis drugs work on only a fraction of patients,” says the study’s first author, Dr. Sam Emaminejad of the University of California, Los Angeles. “Just imagine if you use the wearable sweat sensor with people in clinical drug investigations; we could get a much better insight into how their chloride ions go up and down in response to a drug.” The team plans to continue investigating uses for the device in large-scale clinical studies.

—by Tianna Hicklin, Ph.D.