SAN FRANCISCO: Researchers at Stanford University have designed a home urine test that uses a black box and a smartphone camera to help analyze a standard medical dipstick.
The dipstick test, or color-changing paper test, was invented to test blood sugar in 1956. It now involves 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.
The test seems simple, but do-it-yourself systems on the market can be error prone, said Audrey Bowden, assistant professor of electrical engineering at Stanford. “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. Doctors don’t end up trusting those results as accurate.”
Considering the dipstick as a given, Bowden and Gennifer Smith, a PhD student in electrical engineering, 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 tackled volume control. “If you have too little or too much urine on the dipstick, you’ll get erroneous results,” Smith said. To fix this, they 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, a uniform volume of urine is deposited on each of the ten pads at just the right time.
Then, 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 user 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 user 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.
Writing in Lab on a Chip, a journal of the Royal Society of Chemistry, the researchers said they would like to design an app that would do the analysis on the phone and then send results directly to the doctor.