A Quick Test for Blood Clots

Life-threatening blood clots can form in anyone who sits on a plane for a long time, is confined to bed while recovering from surgery, or takes certain medications.

There is no fast and easy way to diagnose these clots, which often remain undetected until they break free and cause a stroke or heart attack. However, new technology from MIT may soon change that: a team of engineers has developed a way to detect blood clots using a simple urine test.

The noninvasive diagnostic, described in a recent issue of the journal ACS Nano, relies on nanoparticles that detect the presence of thrombin, a key blood-­clotting factor. Such a system could be used to monitor patients who are at high risk for blood clots, says ­Sangeeta Bhatia, senior author of the paper and a professor of health sciences and technology and of electrical engineering and computer science.

Blood clotting is produced by a complex cascade of protein interactions, culminating in the formation of fibrin, a fibrous protein that seals wounds. Thrombin controls the last step of this process—the conversion of fibrinogen to fibrin.

Bhatia’s new test uses iron oxide nanoparticles, which the Food and Drug Administration has approved for human use, coated with peptides (short proteins) that are specialized to interact with thrombin. After being injected into mice, the nanoparticles travel throughout their bodies. When the particles encounter thrombin, the thrombin cleaves the peptides into fragments that are then excreted in the animals’ urine.

Once the urine is collected, the protein fragments can be identified by treating the sample with antibodies that latch onto them. The researchers showed that the quantity of these fragments found in the urine is directly proportional to the level of blood clotting in the mice’s lungs.

Bhatia says she envisions this test being used to screen patients who come to the emergency room complaining of symptoms that might indicate a blood clot, allowing doctors to rapidly triage such patients and determine if more tests are needed.

Another application is monitoring patients who are at high risk for a clot—for example, people who have to spend a lot of time in bed after an operation. The particles could also be adapted to monitor and diagnose cancer, or to track liver, pulmonary, and kidney fibrosis, Bhatia says.