What if we could monitor patients in the future without taking blood samples every time? TU/e researcher Sophie Adelaars investigated a promising alternative: measuring biomarkers in sweat and saliva. This week, she defended her thesis at the Department of Electrical Engineering.
Source: Cursor / Martina Silbrníková
Adelaars conducted her research in collaboration with Philips and the Catharina Hospital, as part of an international consortium. The project focuses on developing a sensor that measures biomarkers - concentrations of various substances - in sweat. Based on these measurements, we could monitor patients' health status and disease progression.
"This method can offer great advantages over traditional blood sampling, as it's less invasive and doesn't require medical personnel for collection," she says. A sweat sensor, which patients can wear on their skin 24/7, has the potential to continuously - and even remotely - monitor their health.
Capture and analyze
"Sweat normally comes out only in small amounts, so it's not easy to collect it," Adelaars explains. "That's why we use pilocarpine - a substance that stimulates the sweat glands - to locally generate more sweat. We can then collect and analyze that."
This method isn't entirely new. Twenty years ago, for example, it was already used to measure chloride concentrations in babies as an indicator of increased risk of cystic fibrosis. Later, however, these sweat measurements were replaced by DNA testing.
"The idea of sweat testing has been around for a while and technically it's possible, but in medical practice it's not used for anything," says the PhD candidate.
This is mainly because we still know surprisingly little about this bodily fluid. Her first research question was therefore: what exactly can we measure in sweat? Followed by: in which group of patients can that information say something about their health or course of disease? Only when we can answer these questions will a sweat sensor become a useful tool in clinical practice.
Saliva
In addition to sweat, Adelaars examined another bodily fluid that can give us valuable information: saliva. Saliva is also easier to collect than blood, although there are some snags. "Things like oral health or food particles can influence the measurement results," she says.
"That's why we established a protocol. The patients weren't allowed to eat, drink, or brush their teeth for half an hour before the measurement." To collect saliva, the patient must chew on a cotton ball for a minute. The cotton ball is then centrifuged and the saliva collected.
Cognitive testing
In addition to sweat and saliva tests, Adelaars also investigated how cognitive testing can provide a better understanding of a patient's condition.
She focused specifically on the role of the BAMCOG test - a playful and patient-friendly screening tool that assesses cognitive functioning - as a predictor for the likelihood of postoperative delirium (POD).
POD is an acute state of confusion that can occur after surgery. Although temporary, it is a serious complication, especially in elderly or vulnerable patients. Symptoms vary between individuals and can easily go unnoticed by medical staff.
"By performing cognitive testing beforehand, we can identify which patients are at higher risk and anticipate accordingly," explains Adelaars.
Patients with kidney failure
Adelaars started her research by analyzing saliva and sweat to find out exactly what substances they contain.
"You have to consider two things: what you can measure in the lab - the concentrations have to be high enough - and what may be clinically relevant to certain diseases," she explains. Based on those criteria, she selected a number of biomarkers that she investigated in greater detail in further studies.
Two of these are urea and creatinine - both waste substances that are normally filtered out of the blood by the kidneys and are therefore important indicators of kidney function.
"In patients with kidney failure, the kidneys cannot properly dispose of these substances and dialysis takes over that function. Using a device connected to a blood vessel, waste products are filtered out of the blood."
The same patterns
"So before this treatment, the concentrations of these biomarkers in the blood are very high, and afterwards they're very low," she explains. "By measuring the concentrations in sweat and saliva before and after treatment, we wanted to find out if they follow the same patterns."
Her study using the data of real patients shows that the concentrations of urea and creatinine in both sweat and saliva do fall in a similar way as in blood. "This is a very important finding, because it shows that these measurements can be clinically relevant," Adelaars emphasizes.
Remote care
"Now that we've discovered this, we can hopefully monitor these patients better and intervene more quickly when necessary. That way we could prevent patients from becoming dependent on a dialysis machine. Because once that happens, it's hard to get off it again."
A wearable device that takes measurements directly - for example, a sticker on the arm, similar to the glucose meters for diabetes patients - could significantly improve remote care.
To achieve this, a great deal of additional research, development, and testing is needed. Not only do various biomarkers require further study, but it's also necessary to develop accurate measuring devices and integrate remote monitoring into existing care pathways. "A lot is still open," says Adelaars.
Still, she's convinced that it's worth exploring this direction further.
"Technology is developing rapidly. We're getting more and more wearable devices that can take all kinds of measurements. And with an increasing aging population and pressure on the care system, it's important that we have the ability to monitor more people in their homes." She says noninvasive methods present a promising solution in this respect. "Measurements in sweat and saliva aren't only less stressful for the patient, but can also contribute to future-proof health care."
