The University of Washington announced that a team of researchers has developed a prothrombin time/international normalized ratio (PT/INR) blood clotting test that requires only a single drop of blood and a smartphone.  According to the team’s February 11, 2022 paper published in Nature Communications, the test uses a tiny cup containing copper, and a blood clotting agent that is attached to the smartphone below the camera, as shown in the figure below from the paper.

After adding a drop of blood, the smartphone vibrates, causing the blood to react with copper and the agent to form a blood clot, all of which is observed and measured by the camera.  A video of the device is here.

Blood clotting, also known as coagulation, is the process by which blood changes into a gel-like substance to prevent bleeding.  Excessive blood clotting within blood vessels can restrict blood flow, leading to serious conditions like deep vein thrombosis and pulmonary embolisms.  Blood thinners can reduce clotting, but patients must have their blood tested frequently to ensure proper dosage, as too much or too little blood clotting can be life-threatening.

Shyam Gollakota, a University of Washington professor and co-author of the paper, stated:

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.  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. … This is the best of all worlds — it’s basically the holy grail of PT/INR testing.  It makes it frugal and accessible to millions of people, even where resources are very limited.

The research team hopes its new test can be deployed in patients’ homes and resource-limited areas.  A public release of the team’s code can be found here.