An experimental system could ease the burden urine tests put on clinics and primary care doctors. A smartphone camera on top of an easily assembled box captures video and accurately analyzes color changes in a standard paper dipstick.
The simple, color-changing paper tests can measure levels of glucose, blood, protein, and other chemicals, which in turn can indicate evidence of kidney disease, diabetes, urinary tract infections, and even signs of bladder cancer.
The simple test is powerful, but it isn’t perfect: It takes time, costs money, and often gives inconclusive results that require both patient and doctor to book another appointment. Patients with long-term conditions like chronic urinary tract infections must wait for results to confirm what both patient and doctor already know before getting antibiotics. Tracking patients’ progress with multiple urine tests a day is out of the question.
In the past, innovators have created a low-cost way to analyze the urinary dipstick in any setting, even at home.
Although the test seems simple, do-it-yourself systems can be error prone, says Audrey (Ellerbee) Bowden, assistant professor of electrical engineering at Stanford University.
“You think it’s easy—you just dip the stick in urine and look for the color change, but there are things that can go wrong,” she says. “Doctors don’t end up trusting those results as accurate.”
Writing in Lab on a Chip, Bowden and Gennifer Smith, a PhD student in electrical engineering, detail their new low-cost, portable device that would allow patients to get consistently accurate urine test results at home, easing the workload on primary care physicians.
Other do-it-yourself systems are emerging, but the Stanford engineers think their approach is inexpensive and reliable, in part because they base their system on the same tried and trusted dipstick used in medical offices.
Fool-proofing three ways
Invented to test blood sugar in 1956, the standard dipstick test is now a paper strip with 10 square pads. Dipped in a sample, each pad changes color to screen for the presence of a different disease-indicating chemical. After waiting the appropriate amount of time, a medical professional—or, increasingly, an automated system—compares the pad shades to a color reference chart for results.
Considering the dipstick as a given, Bowden and Smith designed a system to overcome three main potential errors in a home test: lighting, volume control, and timing.
As a color-based test, the dipstick needs consistent lighting conditions. The same color can look different depending on its background, so Smith and Bowden created a black box that covers the dipstick. Its flat, interlocking parts make it easy to mail, store, and assemble.
They also tackled volume control. “If you have too little or too much urine on the dipstick, you’ll get erroneous results,” Smith says.
To fix this, the engineers designed a multi-layered system to load urine onto the dipstick. A dropper squeezes urine into a hole in the first layer, filling up a channel in the second layer and ten square holes in the third layer. When the third layer is inserted into the black box, some clever engineering ensures that a uniform volume of urine is deposited on each of the ten pads on the dipstick at just the right time.
Finally, a smartphone is placed on top of the black box with the video camera focused on the dipstick inside the box. Custom software reads video from the smartphone and controls the timing and color analysis.
To perform the test a person would load the urine and then push the third layer into the box. When the third layer hits the back of the box, it signals the phone to begin the video recording at the precise moment when the urine is deposited on the pads.
Timing is critical to the analysis. Pads have readout times ranging from 30 seconds to 2 minutes. Once the two minutes are up, the person can transfer the recording to a software program on their computer. For each pad, it pulls out the frames from the correct time and reads out the results.
An app for that
In the future, the engineers would like to design an app that would do the analysis on the phone and then send results directly to the doctor.
Meanwhile, they are working with the Stanford Office of Technology Licensing to see whether and how the idea might be commercialized, either as a home test in developed nations or as a baseline medical instrument in areas that don’t have easy access to well-stocked clinics.
“It’s such a hassle to go into the doctor’s office for such a simple test,” says Smith. “This device can remove the burden in developed countries and in facilities where they don’t have the resources to do these tests.”
Funding for this research came from the National Institutes of Health, the Rose Hills Foundation Graduate Engineering Fellowship, the Electrical Engineering Department New Projects Graduate Fellowship, the Oswald G. Villard Jr. Engineering Fellowship, the Stanford Graduate Fellowship, and the National Science Foundation Graduate Research Fellowship.
Source: Shara Tonn for Stanford University