Researchers from the University of Washington have developed a blood clotting test using a single drop of blood and a smartphone vibration motor and camera.
Blood clots develop naturally to stop bleeding when someone is injured. However, blood clotting in patients with medical issues can lead to strokes or heart attacks. Researchers have developed a new blood clotting test using smartphone technology that determines how well the blood clots.
Patients with medical issues that are susceptible to blood clots often take blood-thinning medications, such as warfarin, that makes it harder for blood to clot. This medication is not perfect and requires patients to be tested frequently to ensure their blood is in the correct range. The process involves a visit to a clinical laboratory or an at-home testing system which can prove to be costly.
The research team have developed a blood clotting test that comprises a plastic attachment that holds a tiny cup beneath a phone’s camera, which in conjunction with a smartphone vibration motor, can test how well blood clots.
The team published their findings in Nature Communications.
How does the blood clotting test work?
The blood clotting test works by individuals adding a drop of blood to the cup, which contains a small copper particle and a chemical that starts the blood-clotting process. Then, the phones vibration motor shakes the cup whilst the camera monitors the movement of the particle, which slows down and then stops moving as the clot forms. The researchers revealed that this method falls within the accuracy range of standard instruments of the field.
“Back in the day, doctors used to manually rock tubes of blood back and forth to monitor how long it took a clot to form. This, however, requires a lot of blood, making it infeasible to use in home settings,” said senior author Shyam Gollakota, UW professor in the Paul G. Allen School of Computer Science & Engineering. “The creative leap we make here is that we’re showing that by using the vibration motor on a smartphone, our algorithms can do the same thing, except with a single drop of blood. And we get accuracy similar to the best commercially available techniques.”
Doctors can rank blood clotting ability using two numbers:
- The time it takes for the clot to form, what is known as the “prothrombin time” or PT,
- A ratio calculated from the PT that allows doctors to more easily compare results between different tests or laboratories called the “international normalised ratio” or INR.
“Most people taking this medication are taking it for life. But this is not a set-and-forget type of thing — in the US, most people are only in what we call the ‘desirable range’ of PT/INR levels about 64% of the time,” said co-author Dr Kelly Michaelsen, assistant professor of anesthesiology and pain medicine in the UW School of Medicine. “This number is even lower — only about 40% of the time — in countries such as India or Uganda where there is less frequent testing. How can we make this better? We need to make it easier for people to test more frequently and take ownership of their health care.”
Patients who can monitor their PT/INR levels from home would only need to go to see a clinician if the test suggested they were outside of that desirable range, Michaelsen said.
Offering an inexpensive, accessible device
The researchers wanted to design an inexpensive blood clotting test device that could work similarly to how at-home blood sugar monitors work for people with diabetes: A person can prick their finger and test a drop of blood.
“We started by vibrating a single drop of blood and trying to monitor waves on the surface,” said lead author Justin Chan, a UW doctoral student in the Allen School. “But that was challenging with such a small amount of blood.”
The team added a small copper particle because its motion was so much more reliable to track.
“As the blood clots, it forms a network that tightens. And in that process, the particle goes from happily bouncing around to no longer moving,” Michaelsen said.
To calculate PT and INR, the phone collects two-time stamps: first when the user inserts the blood and second when the particle stops moving.
“For the first timestamp, we’re looking for when the user inserts a capillary tube containing the sample in the frame,” Chan said. “For the end of the measurement, we look directly at the interior of the cup so that the only movement within those frames is the copper particle. The particle stops moving abruptly because blood clots very quickly, and you can observe that difference between frames. From there, we can calculate the PT, and this can be mapped to INR.”
The researchers tested this method on three different types of blood samples. As a proof of concept, the team started with plasma, a component of blood that is transparent and therefore easier to test. The researchers tested plasma from 140 anonymised patients at the University of Washington Medical Center. The team also examined plasma from 79 patients with known blood clotting issues. For both these conditions, the blood clotting test had results similar to commercially available tests.
Mimicking the at-home experience
To mimic what a patient at home would experience, the team then tested whole blood from 80 anonymised patients at both Harborview and the University of Washington medical centres. This test also yielded results that were in the accuracy range of commercial blood clotting tests.
The blood clotting test device is still in a proof-of-concept stage. The researchers have publicly released the code and are exploring commercialisation opportunities as well as further testing. For example, currently, all these tests have been done in the lab. The next step is to work with patients to test this system at home. The researchers also want to see how the system fares in more resource-limited areas and countries.
“Almost every smartphone from the past decade has a vibration motor and a camera. This means that almost everyone who has a phone can use this. All you need is a simple plastic attachment, no additional electronics of any kind,” Gollakota said. “This is the best of all worlds — it’s the holy grail of PT/INR testing. It makes it frugal and accessible to millions of people, even where resources are very limited.”
