A New Blood Clotting Test

Blood clotting will save your life when it seals a cut. But thrombosis—the formation of a clot inside a non-leaking blood vessel—can lead to potentially lethal consequences such as embolism, stroke, and heart attack. Now a Japanese research team reports a technique for measuring coagulation that could form the basis of a high-throughput assay for a thrombosis risk factor (Anal. Chem., DOI: 10.1021/ac101927n).

Blood is an enormously complex fluid, and the factors that promote clot formation inside vessels are manifold. They include narrowed veins caused by obesity, arteries injured by surgery, and certain kinds of cancer. Blood itself also can increase risk of thrombosis if it is hypercoagulable, or prone to excessive clotting.

Currently doctors use a variety of tests to assess hypercoagulability in blood. Yoshihito Hayashi of Sony Corporation and colleagues wanted to develop a system with a combination of features not available together in current tests: a technique that did not require adding an external clotting agent and one amenable to high-throughput testing.

They turned to dielectric spectroscopy, which can analyze multiple samples at once. The technique monitors blood by quantifying its permittivity, a measure of how much electrical energy it can store. Previous research had shown that as blood clots, its permittivity changes.

To test the feasibility of the method, the team first built a one-sample device. It holds the sample in a cylinder 2 mm long and 9 mm in diameter between two electrodes that apply an electric field. Because a material's permittivity changes with the applied field's frequency, the team looked at a wide electromagnetic spectrum and settled on a single frequency with the best response.

After it's drawn, human blood will slowly clot on its own. (When you donate blood, the phlebotomist adds citrate to your blood to prevent clotting.) The researchers measured changes in permittivity to determine how long whole blood from healthy people took to clot. The resulting coagulation times matched results from a standard coagulation test.

Biophysicist Valerica Raicu of the University of Wisconsin, Milwaukee, calls the study "remarkable." He says it is the first measurement of coagulation time in human blood with dielectric spectroscopy. The result is a "promising advance," says physicist Cesare Cametti of the University of Rome: "It will produce significant improvements in blood analysis."