Researchers design blood clotting test using smartphone

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Researchers at the University of Washington have developed a blood clotting test using a single drop of blood and a vibration motor and smartphone camera.

Blood clots develop naturally to stop bleeding when someone is hurt. However, blood clotting in patients with medical conditions can lead to strokes or heart attacks. Researchers have developed a new blood clotting test using smartphone technology that determines how well blood clots.

Patients with medical conditions that can cause blood clots often take blood thinners, such as warfarin, which make it harder for the blood to clot. This drug 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 home testing system which can be expensive.

The research team has developed a blood clotting test that includes a plastic attachment that holds a small cup under a phone’s camera, which, in conjunction with a smartphone vibration motor, can test blood clotting. blood.

The team published their findings in Communication Nature.

How does the blood coagulation test work?

The blood clotting test involves adding a drop of blood to the cup, which contains a small particle of copper and a chemical that triggers the blood clotting process. Then the phone’s vibration motor shakes the cup while the camera monitors the movement of the particle, which slows and then stops as the clot forms. The researchers revealed that this method is within the precision range of standard instruments in the field.

“Back then, doctors used to manually shake blood tubes back and forth to monitor how long it took for a clot to form. However, it requires a lot of blood, which makes it impossible to use at home,” said lead author Shyam Gollakota, a UW professor at the Paul G. Allen School of Computer Science & Engineering. “The creative leap we’re making here is that we’re showing that by using a smartphone’s vibration motor, our algorithms can do the same thing, except with a single drop of blood. And we get an accuracy similar to the best commercially available techniques.

Doctors can classify blood clotting ability using two numbers:

  • The time it takes for the clot to form, called the “prothrombin time” or PT,
  • A ratio calculated from the PT that makes it easier for doctors to compare results between different tests or laboratories called the “international normalized ratio” or INR.

“Most people who take this drug take it for life. But that’s not a set-it-and-forget-it thing – in the US, most people are only within 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 at the UW School of Medicine. “That number is even lower – only around 40% of the time – in countries like India or Uganda where testing is less frequent. How can we make it better? We need to empower people to get tested more frequently and take ownership of their health care. »

Patients who can monitor their PT/INR levels at home would only need to see a clinician if the test suggested they were outside this desirable range, Michaelsen said.

Offer an inexpensive and accessible device

The researchers wanted to design an inexpensive blood clotting testing device that could work similarly to home blood glucose monitors 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 the waves on the surface,” said lead author Justin Chan, a UW doctoral candidate at the Allen School. “But it was difficult with such a small amount of blood.”

The team added a small copper particle because its movement 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 bouncing happily to not moving anymore,” Michaelsen said.

To calculate PT and INR, the phone collects two timestamps: the first when the user inserts the blood and the second when the particle stops moving.

“For the first timestamp, we’re looking for when the user inserts a capillary tube containing the sample into the frame,” Chan said. “For the end of the measurement, we look directly inside the cup so that the only movement in these frames is the copper particle. The particle suddenly stops moving because the blood is coagulating very quickly, and you “You can see this difference between the images. From there, we can calculate the PT, and that can be mapped to the 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 anonymized patients at the University of Washington Medical Center. The team also examined plasma from 79 patients with known blood clotting problems. For both of these conditions, the blood clotting test gave similar results to commercially available tests.

Mimicking the experience at home

To mimic what a patient at home would experience, the team then tested whole blood from 80 anonymized patients at Harborview and University of Washington Medical Centers. This test also gave results that were within the accuracy range of commercial blood clotting tests.

The blood coagulation test device is still at the proof-of-concept stage. Researchers have made the code public and are exploring commercialization opportunities along with further testing. For example, currently, all these tests have been carried out in the laboratory. The next step is to work with patients to test this system at home. The researchers also want to see how the system performs in regions and countries with more limited resources.

“Almost every smartphone of the last decade has a vibration motor and a camera. This means almost anyone who has a phone can use it. All you need is a simple attachment plastic, no additional electronics of any kind,” Gollakota said. “It’s the best of both worlds – it’s the holy grail of PT/INR testing. This makes it frugal and accessible to millions of people, even where resources are very limited.

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