A smartwatch can tell a lot about a person’s health, but for guarding against big threats like diabetes and heart disease, blood tests remain the gold standard – for now.
Someday, a wearable patch could give patients and doctors the same information, minus the poke in the arm and the schlep to the medical lab.
The patch will track markers in interstitial fluid.
Continuous glucose monitors have already provided this glimpse into the future, by using interstitial fluid to track blood glucose levels in real time.
Now scientists are asking: What else could this tech help us measure?
“The vision is eventually to develop a lab under the skin,” said Joseph Wang, PhD, professor of nanoengineering at the University of California San Diego.
The result:
How does it work?
Sweat and saliva may be easier to get to, but interstitial fluid is a better mirror for blood. It leaks from tiny blood vessels (capillaries), and it carries nutrients to and removes waste from your skin.
To capture this fluid, each monitor has either a tiny wire or an array of less-than-a-millimeter-long microneedles that penetrate the skin for days, weeks, or however long you wear it. “You don’t feel it,” Dr. Wang said. “Once you place it on the skin, you forget about it.”
The microneedles or wires are made from a polymer that sucks up the fluid, which flows to a biochemical sensor targeting the marker you want to measure.
The earliest patents for this technology date back to the 1990s (the first wearable glucose monitors for home use rolled out in the 2000s), but sensors have come a long way since then, becoming smaller, more accurate, and more sophisticated.
Glucose sensors use an enzyme that reacts to glucose to reveal its concentration in the blood. Researcher Jason Heikenfeld, PhD, and his team at the University of Cincinnati focus on “aptamers,” short single strands of DNA that bind to target molecules. “You can leverage the body’s own ability to generate stuff to grab a needle in a haystack,” he said.
The bigger picture
As our population ages and health care costs spiral, and our medical infrastructure and labor force are stretched thin, we’re seeing a push for decentralized medicine, Dr. Heikenfeld said. Like other at-home monitoring technologies, interstitial fluid sensing promises convenience and better access to care.
“There’s a lot you can do over telemedicine, over the phone,” said Justin T. Baca, MD, PhD, associate professor at the University of New Mexico, Albuquerque. “But we still haven’t figured out how to collect reliable biosamples and analyze them remotely.”
Unlike a traditional blood test, which gives a health snapshot for a single point in time, these devices track data continuously, revealing trends and helping you spot oncoming threats earlier.
Take ketones, for example. Dr. Baca and others are using interstitial fluid to continuously detect ketone levels in the blood, potentially enabling us to catch diabetic ketoacidosis sooner.
“It’s potentially like an early warning sign that somebody needs to get either checked out or get rehydrated or get some insulin; kind of an early diagnostic to avoid hospital visits later on,” Dr. Baca said.
Here’s what else this tech could help us do:
Chronic disease management
Seeing the health impact of medication and diet in real time could motivate patients to stick to their treatment plans, Dr. Heikenfeld said. Researchers in Taiwan are developing a test that could help people with chronic kidney disease track levels of cystatin C, a protein that goes up as kidney function declines. Heart disease patients could watch their cholesterol levels drop over time, and of course, diabetes patients can already track glucose.
Prescription drug monitoring
Providers could monitor drug levels in a patient’s body – like antibiotics for an infection – to see how it’s being metabolized, and adjust the dose as needed, Dr. Heikenfeld said.
Stress and hormone therapy
Interstitial fluid could help us measure hormone levels, such as the stress hormone cortisol.
Scientists in the United Kingdom and Norway developed a waist-worn device that collects interstitial fluid samples continuously for up to 3 days. In their study, samples were sent out for analysis, but someday the device could be equipped with a sensor to monitor a single hormone in real time, said study author Thomas Upton, PhD, a clinical research fellow at the University of Bristol in England. “There is a lot of interest in real-time cortisol monitoring,” he said.
Among those who could benefit: patients with hormone deficiencies, night shift workers with disturbed circadian rhythms, or anyone who wants to keep tabs on their stress response.
Human performance and wellness
Athletes could use glucose and lactate monitors to optimize training, recovery time, and diet. For those on the keto diet, a monitor could help them adjust their carb intake based on their ketone levels. Abbott’s Analyte Ventures group is working on blood alcohol sensors, helpful to anyone who wants to avoid overindulging.